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Best Practice & Research Clinical Endocrinology & Metabolism
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Clinical Endocrinology & Metabolism
Familial predisposition to adrenocortical tumors: Clinical and biological features and management strategies
Raul C. Ribeiro, MD, Professor a,b,d,*, Emilia M. Pinto, PhD, Visiting Scientist b,c, Gerard P. Zambetti, PhD, Professor c,d
a Department of Oncology, St. Jude Children’s Research Hospital, Memphis, TN, USA
b International Outreach Program, St. Jude Children’s Research Hospital, Memphis, TN, USA
” Department of Biochemistry, St. Jude Children’s Research Hospital, Memphis, TN, USA
d Department of Pediatrics, University of Tennessee College of Medicine, Memphis, TN, USA
Keywords: Familial cancer syndromes Adrenocortical tumors Management of adrenocortical tumors
The incidence of adrenocortical tumors (ACTs) is increased in several familial cancer syndromes resulting from abnormalities in genes that encode transcription factors implicated in cell prolif- eration, differentiation, senescence, apoptosis, and genomic instability. These include P53, MEN1, APC, and PRKAR1A. Adenomas are the most common ACTs, but adrenocortical carcinomas occur rarely as well. The clinical manifestations of ACTs, which result from increased secretion of adrenocortical hormones, are similar in the familial and sporadic forms of the disease. However, their management may differ because of unique aspects of the consti- tutional syndromes. The analysis of gene expression profiles of ACTs in these constitutional syndromes have contributed to our understanding of adrenal tumorigenesis and revealed new molecular diagnostic and prognostic markers and candidate genes for targeted therapies. This chapter summarizes the clinical and biological features, pathogenesis, and management strategies for ACTs that develop in patients with familial cancer syndrome.
@ 2010 Published by Elsevier Ltd.
Introduction
Adrenocortical tumors (ACTs) are relatively common in clinical practice.1 Results from necropsy studies suggest that the average prevalence of ACTs is 2.3% (range, 1-8.7%).2 Consistent with these observations, a retrospective review of ACTs discovered incidentally during imaging evaluations for
* Corresponding author. Department of Oncology, MS 721, St. Jude Children’s Research Hospital, 262 Danny Thomas Place, Memphis, TN 38105-3678, USA. Tel .: +1 901 595 3694; fax: +1 901 595 5319. E-mail address: raul.ribeiro@stjude.org (R.C. Ribeiro).
1521-690X/$ - see front matter @ 2010 Published by Elsevier Ltd. doi: 10.1016/j.beem.2010.03.002
medical conditions not primarily associated with an adrenal pathology found a similar percentage (4.4%).3 Adrenocortical adenomas are the most common histopathologic diagnosis among these clin- ically silent adrenal masses (incidentalomas). Other histopathologic diagnoses include nodular hyperplasia, myelolipoma, lipoma, lymphoma, angiomyelolipoma, and adrenocortical carcinoma.4 Although most individuals who have ACTs do not suffer from other medical conditions, some tend to carry inherited gene mutations that predispose them to ACTs. These genetic abnormalities can cause a spectrum of clinical manifestations from endocrine syndromes to familial cancer syndromes.
Familial cancer syndromes are defined when multiple members of a family inherit gene mutations that predispose them to one or more types of cancer. In these families, adult-onset cancer develops at a younger age, and patients typically present with multiple primary sites of disease and/or bilateral involvement of paired organs.5 Familial cancer syndromes account for a relatively small percentage of all human cancers. For decades, clinicians suspected that certain tumors (i.e., those of the retina, breast, adrenal gland, and colon) had a genetic basis, because they showed Mendelian segregation in some families. More recently, extensive genome-wide linkage analysis led to the discovery of several specific germline mutations in tumor suppressor genes such as P53 that act according to Knudson’s “two hit” hypothesis (i.e., both alleles of the gene must be altered before cancer can arise)6 and explain familial cancer segregation. Remarkably, although persons carrying mutations in cancer-susceptibility genes have increased predisposition to cancer, most do not have other medical problems and lead normal productive lives including reproductive function.
Our increased understanding of the molecular pathways that trigger cancer and the development of novel methods that allow us to investigate those pathways and the function of cancer-susceptibility genes regulated by them has led to the discovery of a host of genes whose mutation could increase a person’s predisposition to cancer. Moreover, results from genotypic studies and cancer phenotypic association studies have revealed that some gene mutations and common genetic polymorphic vari- ants might synergize to modulate cancer susceptibility. Thus, many tumors originally considered sporadic may also have an inherited basis. Finally, in constitutional syndromes such as Beck- with-Wiedemann syndrome (BWS), an increased susceptibility to ACTs has been also noted. In this chapter, we will describe the genetic and biologic features of ACTs and discuss their pathogenesis, management, and outcome and familial disorders associated with ACTs.
Genetic basis of familial predisposition to adrenocortical tumors
Mutations in P53 (Li-Fraumeni and Li-Fraumeni-like syndromes)
Epidemiology of ACTs in carriers of P53 mutations
In the late 1960s, Li et al. described four families with an autosomal-dominant pattern of several malignancies in the children and adults.5,7 These families were classified as having Li-Fraumeni syndrome. Of the 44 cases of cancer that occurred among family members younger than 15 years, four (9%) were ACT.5 This frequency is much higher than that observed in the general population of persons younger than 15 years (0.3 cases per million), and ACTs account for less than 0.5% of all pediatric solid malignancies. In 1990, Malkin et al8 discovered that germline mutations in the P53 gene account for the cancer-dominant segregation pattern seen in families with Li-Fraumeni syndrome. Further studies of more families who fulfilled the Li-Fraumeni criteria suggested that 50% of carriers of mutated P53 experience cancer by 30 years of age, and 90% by 60 years.9 Despite the close association between germline P53 mutations and cancer, when all forms of cancer are considered, only about 1% of patients carry germline P53 mutations. An exception is seen in pediatric ACTs; more than 50% of affected children carry a germline P53 mutation. Moreover, the type of P53 mutations in children with ACT appears to differ from those found in carriers with other tumors. For example, data from the Inter- national Agency for Cancer Research P53 registry shows that about 80% of patients with breast cancer who carry P53 mutations belong to a family with Li-Fraumeni syndrome. In those cases, the mutations typically render the P53 protein inactive. Conversely, only 15% of children with ACT are from families with Li-Fraumeni syndrome families (http://www-p53.iarc.fr/). Many children with ACTs carry low- penetrant P53 mutations that encode partially functional P53 protein.10,11 Therefore, children with ACT, regardless of their family history of cancer, should be considered germline P53 mutation carriers.12
Importantly, the life-long probability of cancer developing in carriers of low-penetrant germline P53 mutations is presently unknown.
Biology of P53
Human P53 is a 53-kDa nuclear phosphoprotein encoded by a 20-Kb gene containing 11 exons and 10 introns13 that is located on the small arm of chromosome 17.14 This gene belongs to a highly conserved gene family containing at least two other members, P63 and P73. Wild-type TP53 protein contains 393 amino acids and is composed of several structural and functional domains: an amino-terminal domain (residues 1-42) required for transactivation and interaction with various transcription factors including acetyltransferases and MDM2 and a proline-rich region with multiple copies of the PXXP sequence (residues 61-94, where X is any amino acid). The proline-rich region plays a role in P53 stability, which is regulated by MDM2. A central core domain (residues 102-292) is required for sequence-specific DNA binding, and a C-terminal region (residues 301-393) functions as a negative regulatory domain con- taining an oligomerization domain (residues 324-355), a strongly basic C-terminal regulatory domain (residues 363-393), a nuclear localization signal sequence, and three nuclear export signal sequences.15
The P53 tumor suppressor is a transcription factor that regulates the expression of a diverse set of target genes (e.g., p21CP1, PUMA, TSP1) that control cell proliferation, cell survival, DNA repair, angio- genesis, and senescence.16 DNA damage and other forms of cellular stress lead to P53 stabilization and activation. P53 blocks cell cycle progression in G1 and G2/M cell cycle phases, thereby preventing the replication of potentially tumor-promoting DNA lesions and the division of abnormal cells. Alterna- tively, activated P53 can trigger apoptosis to eliminate the damaged cell.
P53 mutations that inactive the protein are the most common genetic alterations found in human cancers, and there is growing evidence that inactivation of the P53 pathway occurs in most tumors.17 Point mutations are scattered over more than 250 codons and are common in many forms of human cancer. Approximately 95% of these mutations occur in the core DNA-binding domain. Furthermore, 75% of the mutations are missense mutations that result in the tumor-associated form of P53 being predominantly full length, with a single amino acid change in the core domain. These mutations usually confer the mutant protein with dominant-negative activity over the remaining wild-type allele, a mechanism that involves hetero-oligomerization of the mutant protein with the wild-type protein.18 In this respect, the P53 gene differs from other tumor suppressor genes such as RB1, APC, and P16, which are frequently inactivated by deletion or nonsense mutations, and from the oncogenes of the RAS family, which are activated by mutation at a few well-defined codons.19 The loss of P53 function by mutation or other means (e.g., overexpression of MDM2) promotes genomic instability and the growth and survival of corrupted cells, as well as the formation of new blood vessels that supply oxygen and nutrients to those abnormal cells.
Studying the relationship between genotype and phenotype is particularly complex in carries of P53 mutations. How P53 is targeted during tumorigenesis determines whether its tumor suppressor activity is partially or fully lost, and the amount of remaining P53 activity affects the tumor phenotype, as P53 has a gradient effect upon tumors.20
Clinical characteristics of pediatric patients with adrenocortical tumors
Influence of P53 mutations. Analyses of the demographics, clinical features, and outcomes of children enrolled in the International Pediatric Adrenocortical Tumor Registry (IPACTR), www.stjude.org/acc revealed no difference in the presenting clinical features of patients who carry germline P53 muta- tions and those who do not.21 In this series, about 80% of patients had a germline P53 mutation. The median age at diagnosis of ACT was 3.2 years. Fewer than 15% were 13 years or older at diagnosis. The incidence was higher among girls than boys (ratio, 1.6:1), and this sex difference increased with age to a ratio of 6.2:1 in adolescents (13-18 years).22
Symptoms of pediatric ACT. Patients with ACTs typically present with endocrine manifestations resulting from an increased production of androgens (virilization) and/or cortisol (hypercortisolism or Cushing syndrome). Hyperestrogenism (feminization) or aldosteronism (Conn syndrome) is rarely seen. Mixed
endocrine syndromes resulting from the secretion of several adrenocortical hormones are also common.22 Substantial endocrine manifestations can be present, even when the tumors are small. In the IPACTR series,21 tumor weight was 200 g or less in 99 of 182 (54.4%) cases. Nonfunctional tumors are more common in older children and adolescents. Pure virilization is much more frequent in very young children.22 Although rare, virilization can be present at birth or detected during the newborn period.23 In occasional cases of apparently nonfunctional ACT, adrenal hormone precursors of low bioactivity can be detected.
In addition to the endocrine clinical manifestations, elevated blood pressure is common in these patients; about 10% experience hypertensive encephalopathy including seizures.24 Abdominal pain or discomfort is a common presenting symptom in patients without endocrine manifestations. ACT has been incidentally detected in fetuses during prenatal ultrasound evaluation.25 Growth disturbances are also common in these patients, most of whom show increased growth velocity and premature epiphyseal closure. Weight loss is not typically present, even in patients with advanced-stage disease.
Clinical evaluations of ACTs. Routine laboratory evaluation for suspected ACT includes the measurement of urinary free cortisol and plasma levels of cortisol, DHEA-S, testosterone, androstenedione, 17-hydroxy progesterone, aldosterone, renin activity, DOC, and other 17-deoxysteroid precursors. This comprehensive panel of tests not only contributes to diagnosis but also provides useful markers for the detection of tumor recurrence.
Several imaging modalities are used to establish the diagnosis of ACT. Computed tomography (CT), sonography, magnetic resonance imaging (MRI), and positron emission tomography (PET) scanning are the most commonly used. Although ultrasound examination has its limitations, it is important for evaluating tumor extension into the inferior vena cava and right atrium. MRI has several advantages over CT, including the absence of ionizing radiation, the capability of imaging multiple planes, and improved tissue contrast differentiation. Fluorodeoxyglucose (FDG)-PET imaging is increasingly used in patients with ACT.26
Diagnosis of ACT is confirmed based on the gross and histologic appearance of tissue obtained surgically. Tumors are classified as adenoma or carcinoma based on several pathologic criteria,27 although even experienced pathologists can find it difficult to differentiate between these two cate- gories.28 In the IPACTR series, about 80% of the cases were classified as carcinoma, and the remaining were classified as either adenomas or undetermined.
Treatment, outcome, and prognosis of patients with adrenocortical tumors
Surgery. Surgical intervention is the mainstay of treatment for ACTs. En bloc resection, which may include the kidney, portions of the pancreas and/or liver, or other adjacent structures, may be necessary in rare cases of large, locally invasive tumors. Laparoscopic tumor resection has been extensively used in adults with relatively small adrenal tumors.29 Due to the friability of these tumors and the potential for tumor spillage, open adrenalectomy is recommended in children with ACTs. The role of regional lymph node dissection in pediatric ACT has not been defined, but it is currently being evaluated by the Children’s Oncology Group.
Surgical procedures also play a crucial role in treating recurrent local and distant disease. Multiple surgical resections may be necessary to render patients free of disease. This aggressive approach is associated with prolonged survival. Surgical procedures require careful and precise perioperative plan- ning. All patients with a functioning tumor are assumed to have suppression of the contralateral adrenal gland; therefore, steroid replacement therapy is given until that gland recovers. The patient’s electrolyte balance, hypertension, surgical wound care, and infectious complications must also be monitored. Infiltration of the vena cava may make radical surgery difficult in some cases, although successful complete resection of the tumor thrombus has been reported with cardiopulmonary bypass.30
Chemotherapy. The role of chemotherapy in the management of childhood ACT has not been estab- lished. Mitotane has been used extensively and is recommended for adults with ACT,31,32 but its efficacy in children remains unknown. Adults treated with mitotane show varied responses (15-60%), which in
part reflects the pharmacokinetics of the drug. Evidence indicates that tumors respond better when the plasma concentration of mitotane is maintained above 14 mg/L. The most common toxicities of mitotane are nausea, vomiting, diarrhea, and abdominal pain. Less frequent reactions include somnolence, lethargy, ataxic gait, depression, and vertigo. Another shortcoming of mitotane treatment is that it substantially alters steroid hormone metabolism; thus, blood and urine samples cannot be used to measure steroid levels, which are typically monitored as markers of tumor relapse.
Mitotane should be considered an experimental agent in the treatment of pediatric ACTs. Other chemotherapeutic agents (e.g., 5-fluorouracil, etoposide, cisplatin, carboplatin, cyclophosphamide, doxorubicin, and streptozocin) have been used alone or in combination to treat ACT with varied results.33 The combination used most often in pediatrics and currently being evaluated prospectively by the Children’s Cancer Group includes mitotane, cisplatin, etoposide and doxorubicin.
Because current chemotherapeutic approaches to treating ACTs are inadequate, the development of newer compounds targeting specific cellular pathways is appealing.34,35 A Phase I trial of an IGF-1R blocker has been initiated in adults and soon is expected to include children. ACT is considered radi- oresistant, though this concept has been recently questioned.36 There have been no studies of the effects of radiotherapy on pediatric ACT. Moreover, because most children with ACT carry a P53 mutation, radiotherapy should be avoided because these patients are at increased risk of treatment- induced second cancers.
Prognosis. In the IPACTR series of 254 patients with known outcomes, 97 (38.2%) died and 157 (61.8%) were alive at a median follow-up of 2.4 years (range, 5 days to 22 years).21 Five patients died of causes unrelated to tumor progression (two died of infection, one of a hypertensive complication, one of massive hemor- rhage during surgery, and one of an unspecified complication). The estimate of 5-year event-free survival (EFS) was 54.2% (95% CI, 48.2-60.2%), and that of overall survival was 54.7% (95% CI, 48.7-60.7%).22
Complete tumor resection is the single most important prognostic indicator; the probability of long- term survival is approximately 75% for children with completely resected ACTs. Patients who have residual disease after incomplete tumor resection have a dismal prognosis. Tumor size has been consistently associated with prognosis of ACT.37,38 IPACTR data showed that among 192 pediatric patients with totally resected ACTs, the EFS estimate for those with tumors weighing more than 200 g was only 39%, and that of patients with smaller tumors was 87%. Children whose tumors produce excess glucocorticoid appear to have a worse prognosis than those whose tumors have solely virilizing manifestations. Classification schemes and disease-staging systems to guide therapy for pediatric patients with ACT are still evolving. A modification of the original ACT staging system published by Sandrini et al. in 199724 includes tumor volume and resectability (Table 1). The analysis of prognostic factors can probably be further refined by adding other predictive factors.39-42
Multiple endocrine neoplasia type I
Epidemiology and pathogenesis of MEN1
Multiple endocrine neoplasia type 1 (MEN1) is a rare autosomal-dominant syndrome characterized by the occurrence of tumors involving two or more endocrine glands. The combined occurrence of tumors of the parathyroid glands, the pancreatic islet cells, and the anterior pituitary is the hallmark of MEN1, which is also referred to as Wermer syndrome. Other tumors associated with the syndrome include adrenocortical adenomas, neuroendocrine carcinoid, facial angiofibromas, collagenomas, and lipomatous tumors.43-45 MEN1 has an estimated prevalence of 0.01 to 2.5 per 1000 persons. Endo- crinopathy and tumors develop in patients most often during their third or fourth decade of life, and the onset of overt disease is rare before 10 years of age.46,47 Although most cases of MEN1 are familial, 8-14% might be sporadic.48 MEN1 is caused by one of several hundred mutations in the MEN1 gene, which is located at chromosome 11q13, spans 9.8 kb, and has 10 exons in the open reading frame.49 Most of the mutations encode truncated forms of the 610-amino acid protein menin.49,50 Menin is widely expressed in endocrine and nonendocrine tissues. MEN1 follows Knudson’s “two-hit” model6: the first hit is a heterozygous MEN1 germline mutation inherited from one parent (familial form) or develops during an early embryonic stage (sporadic form). The second hit is a MEN1 somatic mutation,
| Stage | Clinical features |
|---|---|
| I | Completely resected tumor Small tumor (weight, <100 g; volume, <200 cm3) Normal postoperative hormone levels |
| II | Completely resected tumor Large tumor (weight, ≥100 g; volume, ≥200 cm3) Normal postoperative hormone levels |
| III | Unresectable tumor, gross or microscopic residual disease Tumor spillage Stage I or II tumor features and abnormal postoperative hormone levels Retroperitoneal lymph node involvement |
| IV | Presence of distance metastases |
usually a large deletion that occurs in the remaining wild-type allele. Loss of heterozygosity (LOH) at 11q13 is evident in most cases of familial MEN1. Similarly, tumors may sporadically develop as the two alleles are subsequently inactivated.51
Molecular-partnering studies have identified the transcription factor JUND, which belongs to the activator protein-1 (also known as JUN-FOS) family of early-acting transcription factors, as a direct menin-interacting partner32 and the COMPASS-like complex that has several chromatin-related activities, including histone methyltransferase activity for lysine 4 on histone 3.53 Mechanisms that protect menin from malignant transformation include inhibition of cell proliferation, promotion of apoptosis, and genomic stability.54 No clear correlation between MEN1 genotype and phenotype has emerged to date. The clinical manifestations of MEN1 vary among individuals. The heterogeneity of endocrine abnormalities and susceptibility to various neoplasias in a relatively narrow spectrum of tissues suggest that other epigenetic factors, modifiers, gene products, or a combination thereof contribute to the pathogenesis of this disease.55
Clinical features and management of ACTs in MEN1
Adrenal involvement occurs in about 40% of MEN1 cases. The lesions vary from adrenal hyperplasia, nodularity, to neoplasia.56 In a CT study of the appearance of the adrenal gland in 28 individuals with MEN1, images showed that the adrenal limbs were larger in patients with MEN1 than in the normal cohort. Twenty of 24 (83%) patients had at least one adrenal limb that was larger than 2 standard deviations above the normal mean. The adrenal body was significantly larger in the MEN1 cohort as well. Furthermore, in 17 of the 27 (63%) patients, one or more adrenal nodules was larger than 5 mm. This compares with 0.4-2% in the normal population. The nodules were predominantly focal (88%).57 In patients with MEN1, symptoms are caused by local mass effect or overproduction of a specific hormone by the endocrine tumors. Although symptoms are rarely caused by the malignant progression of the neoplasm, it is the main cause of death in patients with MEN1. Nonfunctioning adenoma is the most common histologic type of adrenocortical nodular lesions, but adrenocortical carcinomas have been observed in MEN1. LOH at 11q13 is present in 10-14% of sporadic adrenocortical adenomas and almost always occurs in sporadic adrenocortical carcinomas.58
Guidelines for management of endocrine tumors in MEN1 have been discussed,45 although no specific recommendations have been made for treating patients with adrenal pathology. Currently, the evaluation and management of ACTs in patients with MEN1 follow the same guidelines as used to treat patients with sporadic masses or ACTs.59
Familial adenomatous polyposis
Epidemiology and biology of FAP
Familial adenomatous polyposis (FAP) is an autosomal-dominant condition associated with the development of hundreds to thousands of polyps in the rectum and colon during early adulthood. If left
untreated, FAP will develop into colorectal cancer (CRC) when the patient reaches 35-40 years of age. CRC is a major cause of cancer mortality and morbidity; about 85% of CRC cases are considered sporadic, and approximately 15% are familial. FAP accounts for less than 1% of all CRC cases.60 Patients with FAP have an increased risk of extraintestinal manifestations such as desmoid tumors, osteomas, epidermal cysts, hepatoblastomas, congenital hypertrophy of retinal pigmented epithelium, adrenal adenomas, and upper gastrointestinal tract polyps.61 Adrenocortical carcinoma has been reported very infre- quently. The incidence of FAP in the population is approximately 1 in 8000 persons. Despite the strong selective disadvantage of the disease, its incidence is maintained by the frequency of new mutations, which cause about 25% of all cases.62
The genetic defect in FAP is a germline mutation in the adenomatous polyposis coli (APC) gene located on band 5q21. The APC gene has three alternative transcripts. The alternative splice forms of APC include alternate exons located 5’ of the missing exon 1. The full-length human APC is a 2843- amino acid protein with a predicted molecular mass of 311 kDa.63 This gene product is a tumor suppressor that plays a pivotal role in Wnt signaling and regulates the degradation of ß-catenin. Wnt signals stabilize a protein complex containing ß-catenin, axin and its analog conductin, and glycogen synthase kinase 3(GSK3B). APC binding to ß-catenin results in ubiquitin-mediated ß-catenin destruction, whereas the loss of APC function increases transcription of ß-catenin targets, including growth-associated genes in conjunction with tissue-coding factors. Moreover, the loss of APC function prevents apoptosis. When combined with increased transcription of ß-catenin, this results in consti- tutive cell growth, adenoma formation, and tumorigenesis. Similarly, mutations in the CTNNB1 gene, which encodes B-catenin, prevent GSK3B-mediated phosphorylation and subsequent ß-catenin degradation and ultimately result in ß-catenin pooling and activation of transcription.64
The Wnt pathway was analyzed in 26 adrenocortical adenomas and 13 carcinomas from adult patients, none of whom had a constitutional or familial cancer syndrome. Abnormal cytoplasmic and/ or nuclear accumulation of ß-catenin was detected in 10 of 26 (38%) adenomas, which showed a focal pattern, and in 11 of 13 (85%) carcinomas, which showed a diffuse pattern. A screen for ß-catenin gene mutations found similar frequencies in adrenocortical adenomas (27%) and carcinomas (31%).65
Clinical features and management of ACTs in FAP
Since the first published case report of a patient with FAP and adrenocortical adenoma in 1912, about 50 cases have appeared in the literature.61 The median age at the time of diagnosis of the adrenal lesion varied from 14 to 70 years, with a median of approximately 40-50 years. The routine use of imaging modalities such as CT and MRI has revealed that the prevalence of adrenal masses that are 1 cm or larger (incidentalomas) is 13% in patients with FAP.66 The clinical presentation and biological behavior of the tumors do not appear to differ from those of incidentalomas occurring in the general population. Most adrenal adenomas do not produce hormones; however, the production of cortisol, aldosterone, or both has been observed. Adrenal carcinomas are rarely associated with FAP.
The clinical concerns of FAP are to determine whether the adrenal mass is overproducing adrenal hormones and whether it has malignant potential. Hormonal assessment and imaging follow-up of lesions larger than 4 cm are indicated to determine whether surgical intervention is warranted.
Carney complex
Epidemiology and biology of the Carney complex
The Carney complex (CNC), which is an inherited autosomal-dominant disorder, was first described in 1985 as the combination of myxomas of the heart and skin, spotty pigmentation (lentiginosis), and endocrine overactivity.67 Cardiac myxomas, which occur in 30-60% of cases, may lead to embolic stroke and/or heart failure.68 Lentigines occur in approximately 70% of CNC cases and are most commonly seen on the face, especially on the lips, eyelids, conjunctiva, and oral mucosa.69 Patients with CNC may present with Cushing syndrome or simultaneous involvement of multiple endocrine glands, including growth hormone-secreting pituitary tumors and gonadal and thyroid neoplasias, as seen in MEN1 and MEN2 syndromes.70
In the original description of CNC by Carney et al, 25% of the cases were classified as familial,70 suggesting an inherited genetic abnormality in the etiology of CNC. Further linkage-analysis studies
revealed that CNC is genetically heterogeneous, and at least two chromosome loci, 2p16 and 17q22-24, are involved.71,72 The CNC1 gene, located at 17q22-24, was identified as the regulatory subunit of protein kinase A (PRKAR1A).72,73 PRKAR1A, a tumor suppressor gene, is a key component of the cAMP- signaling pathway and has been implicated in endocrine tumorigenesis.74 Sixty PRKAR1A mutations have been described; most are 1-bp substitutions, and some are exonic insertions or deletions.75 Germline mutations are observed in about 60% of patients with CNC, and in about 80% of those who have CNC and Cushing syndrome.76 However, phenotypic differences have been observed between patients with PRKAR1A mutations and those without.70 LOH at the 17q22-24 locus occurs in tumors associated with CNC. Moreover, a high frequency of somatic PRKAR1A chromosomal alterations is seen in adrenocortical tissues maintained in culture.75 In a transgenic mouse model of CNC in which Prkar1a is heterozygously inactivated, tumors may develop without allelic loss. The Prkar1a+/- mice exhibit sarcomas that usually have myxomatous features. Tumors that arise in Prkar1a+/- mice do not display LOH, which is consistent with human CNC tumors. Nonetheless, the propensity of Prkar1a+/- mice for extracardiac tumors supports a role of Prkarla as a tumor suppressor.77 Male Prkar1a+/- mice have severely reduced fertility. Like male patients with CNC who are heterozygous for PRKAR1A mutations, these mice have fewer and morphologically abnormal sperm. Elevated protein kinase A activity in male meiotic or postmeiotic germ cells may cause structural defects in mature sperm; this would explain the reduced transmission of PRKAR1A-inactivating mutations by male patients with CNC.78,79 A putative CNC2 oncogene, located at chromosome 2p16 and possibly involved in the pathogenesis of CNC, has not been identified. LOH and copy number alterations of the 2p16 region have been reported in CNC tumors, even in patients with PRKAR1A mutations.70
Clinical features and management of ACTs in CNC
Primary pigmented nodular adrenocortical disease (PPNAD) is a rare disorder that accounts for the Cushing syndrome observed in CNC. PPNAD is usually bilateral and characterized by small pigmented micronodules in the adrenal cortices. It is the most frequent endocrine tumor in individuals with CNC, i.e., it occurs in about 25-30% of these individuals. PPNAD-induced hypercortisolism is observed in children and young adults but peaks during the second decade of life. It rarely occurs in individuals younger than 4 years or older than 40 years.80 Because hypercortisolism may develop slowly in some patients with PPNAD, Cushing syndrome can go undetected for many years. In other cases, cyclic hypercortisolism has been noted.81 Hormonal evaluation of patients with PPNAD shows an elevated urinary level of cortisol and low plasma level of ACTH. Administration of corticotropin-releasing hormone does not stimulate cortisol or ACTH secretion. Moreover, dexamethasone does not suppress cortisol secretion.
In approximately 25% of patients with PPNAD, the adrenal glands appear normal on CT images. In the remaining patients, nodules in one or both glands are visible, the majority of which is smaller than 1 cm. Adrenalectomy is the most common treatment for PPNAD-induced Cushing syndrome.82 Adre- nolytic drugs (e.g., mitotane, aminoglutethimide, and ketoconazole) and antihypertensive drugs have been used to control severe hypercortisolemia and its consequences in preparation for surgery. In a few patients who underwent unilateral adrenalectomy, overt Cushing syndrome has not recurred, despite laboratory evidence of increased cortisol production.83
Beckwith-Wiedemann syndrome/hemihyperplasia
Epidemiology and biology of BWS
Beckwith-Wiedemann syndrome (BWS) is one of the most common overgrowth disorders; BWS occurs in approximately 1:14,000 births and is classically characterized by exomphalos, macroglossia, and gigantism.84 Moreover, individuals with BWS have an increased frequency of malformations including omphalocele, exomphalos, and diastasis recti; hypoglycemia, which occurs in about 50% of newborns with BWS and is caused by islet cell hyperplasia and insulinemia; and visceromegaly involving the liver, spleen, pancreas, kidneys, and adrenals. Fetal adrenocortical cytomegaly is pathognomonic of BWS. Cardiac malformations are found in about 20% of individuals with BWS. Finally, children with BWS have an increased predisposition to embryonal malignancies including Wilms tumor, rhabdomyosarcoma, hepatoblastoma, ACTs, and neuroblastoma. The overall risk of tumor development is 5-7%,85 and about 15% of cases are familial.86
Hemihyperplasia, formerly termed hemihypertrophy, is characterized by asymmetry between the right and left sides of the body to a greater degree than can be attributed to normal variation. It can involve asymmetric growth of the cranium, face, trunk, limbs, and/or digits. Hemihyperplasia can be isolated (IHH) in an otherwise normal individual or can be associated with certain developmental syndromes, such as Beckwith-Wiedemann syndrome, neurofibromatosis, Klippel-Trenaunay-Weber syndrome, and Proteus syndrome.87 IHH is a congenital overgrowth disorder associated with an increased risk for embryonal tumors, mainly Wilms tumor and hepatoblastoma. Epidemiological studies of IHH have shown that the incidence is 1:86,000 live births.88 However, its true prevalence is difficult to determine because minor asymmetry of the limbs often is considered normal.89 IHH appears to be sporadical, although familial cases have been reported.90 Interestingly, it has been suggested that patients with BWS and hemihyperplasia have a higher cancer risk than do children with BWS without limb length discrepancy.91
The molecular basis of BWS syndrome is complex.92 The BWS phenotype is caused by the deregulation of imprinted genes in the 11p15.5 chromosomal region. This region is divided into two functional domains. Domain 1 contains two imprinted genes, H19 and insulin-like growth factor 2 (IGF2). Normally, IGF2 is maternally imprinted, thus IGF2 is expressed only from the paternal allele. Conversely, the H19 is paternally imprinted, hence H19 protein, which modulates the expression of IGF2, is expressed only from the maternal allele.93 Domain 2 contains several imprinted genes, including KCNQ1, KCNQ1OT1, and CDKN1C. Deregulation of these genes can occur through various mechanisms including chromosome region duplications (uniparental disomy), translocations, inver- sions, and microdeletions. DNA methylation changes modulate the expression of IGF2, H19, KCNQ1, and KCNQ1OT1 and mutations at CDKN1C (P57kip2). The P57kip2 gene encodes a cyclin-dependent kinase inhibitor that belongs to the CIP/KIP family of cell cycle regulators. Overexpression of this gene arrests cells in the G1 phase of the cell cycle. A practical model for clinical purposes suggests that increased dosage of growth-promoting genes or decreased dosage of growth-suppressor genes account for the BWS phenotype.94 Accordingly, the paternally expressed gene(s) located on domain 1 (telomeric) of 11p15, such as IGF2, which has a stimulatory effect on cell and tissue growth, is considered pathogenically crucial. Conversely, the maternally expressed gene(s) located on domain 2 (centromeric) of 11p15, such as P57kip2, which encodes a cyclin-dependent kinase inhibitor, would have the similar pathogenetic consequences. Therefore, according to the model, normal development and growth require a balance between growth stimulation by the paternally expressed gene(s) and growth suppression by the maternally expressed gene(s). In BWS, this balance is lost and growth is stimulated.
IHH may be part of the phenotypic spectrum of BWS. Mosaic paternal uniparental disomy for 11p15 was observed in one affected twin in the case of a pair of monozygotic twins who were discordant for IHH.95 Moreover, paternal uniparental disomy of 11p15 was observed in 8 of 51 (16%) patients with IHH, and hypomethylation at KCNQ10T1 (LIT1) was observed in 3 (6%) of these patients.96
Clinical features and management of ACTs in BWS
Because the IGF-signaling pathway abnormalities, including overexpression of IGF2, have been implicated in the pathogenesis of ACTs 86,97 and BWS overgrowth, the incidence of ACTs would be expected to be increased in this syndrome. Moreover, several cases of pediatric ACT with BWS have been reported.98-102 One percent of children with ACT have BWS; however, the prevalence of pediatric ACT in WBS has not been determined. For example, not a single case of ACT was found in a study of 183 patients with BWS followed for 482 patient-years during the first 4 years of life, though 13 cases of cancer were noted.103 Association between ACTs and congenital hemihypertrophy was established by Fraumeni and Miller,104 who reviewed the charts of 62 pediatric patients with ACT. Of those, two (3%) had hemihyperplasia. Other reports have related the association between IHH and ACTs.105,106 Tumor surveillance is typically initiated if BWS is diagnosed or suspected, i.e., abdominal ultrasound assessment of kidney, liver, pancreas, and adrenal glands is recommended quarterly to the age of 8 years. Other tests such as MRI and adrenal hormonal evaluation may become necessary if ultrasound shows a suspicious finding. Because there is no specific genotype-to- phenotype association between IHH and tumor development, all patients with IHH should undergo tumor screening.91
Practice points
1. The relative frequency of childhood adrenocortical tumors (ACT) is increased in certain familial cancer syndromes, in which multiple members of a family inherit gene mutations that predispose them to one or more types of cancer.
2. Patients with ACT typically present with endocrine manifestations resulting from the increased production of androgens (virilization) and/or cortisol (hypercortisolism or Cushing syndrome). The clinical manifestations of ACT are similar in the familial and sporadic forms of the disease.
3. TP53 mutations are the inherited genetic abnormalities most commonly associated with increased ACT frequency in familial cancer syndromes. Mutations of other genes, including MEN1, APC, and PRKAR1A, also increase predisposition to adrenal tumors.
4. There is a cluster of cases of childhood ACT in southern Brazil, where the incidence of ACT is 15 times that in other parts of the world. More than 80% of these patients carry a specific germline TP53 mutation. Their families do not exhibit the classical profile of Li-Fraumeni syndrome.
5. Surgical intervention with en bloc resection is the mainstay of treatment for ACT.
6. Childhood ACTs are classified as adenomas or carcinomas on the basis of several pathologic criteria. However, even experienced pathologists can find it difficult to distinguish between these two categories. In our series, about 80% of the cases were classified as carcinomas, and the remainder were classified as either adenomas or undetermined.
7. ACT is chemosensitive, but the role of chemotherapy (including mitotane) in the manage- ment of this disease has not been established.
8. Disease stage that incorporates tumor size is the most important predictor of outcome. Completely resected small tumors are associated with excellent outcome. The prognosis is dismal for patients who have residual disease after incomplete tumor resection or who have metastatic disease.
Research agenda
1. Development of pediatric ACT xenograft models to study the biology of the tumors and to evaluate conventional and new drugs for the management of this disease.
2. Identification of additional gene mutations and metabolic pathways that contribute to childhood adrenal cortex tumorigenesis.
3. Development of new laboratory methods to improve existing prognostic classification groups.
4. Implementation of an ACT registry for the long-term follow-up of children with ACT and for genotype-phenotype association analyses of their relatives.
5. Testing of new drugs that target key pathway gene products known to be involved in the tumorigenesis of ACT.
Acknowledgements
This work was supported in part by grant CA-21765 from the National Institutes of Health (U.S. Department of Health and Human Services), by a Center of Excellence grant from the State of Ten- nessee, and by the American Lebanese Syrian Associated Charities (ALSAC). We thank Angela J. McArthur for expert scientific review of the manuscript.
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