Impact of 18F-FDG PET/CT on the management of adrenocortical carcinoma: analysis of 106 patients
Satoshi Takeuchi . Aparna Balachandran . Mouhammed Amir Habra · Alexandria T. Phan . Roland L. Bassett Jr. . Homer A. Macapinlac . Hubert H. Chuang
Received: 27 March 2014 / Accepted: 5 June 2014 C Springer-Verlag Berlin Heidelberg 2014
Abstract
Purpose Adrenocortical carcinoma (ACC) is a rare and ag- gressive malignancy. Limited data are available about on value of 18F-FDG PET/CT in ACC. We evaluated the impact of PET/CT on the management of ACC.
Methods We performed a retrospective review in patients with ACC who had undergone PET/CT. The impact of PET/ CT on the management plan was evaluated by comparing the findings on PET/CT to the findings on contrast-enhanced CT. The sensitivity, specificity, and accuracy of each form of imaging were calculated. The correlations between PET/CT parameters, including maximum standardized uptake value (SUVmax), total lesion glycolysis, and decline in SUV max after chemotherapy, and clinical outcome were evaluated.
These results were presented in part at the Society of Nuclear Medicine and Molecular Imaging Annual Meeting, Vancouver, British Columbia, 8-12 June 2013.
S. Takeuchi () . H. A. Macapinlac . H. H. Chuang Department of Nuclear Medicine, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd., Unit 1483, Houston, TX 77030, USA
e-mail: sato825@gmail.com
A. Balachandran
Department of Diagnostic Radiology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
M. A. Habra Department of Endocrine Neoplasia and Hormonal Disorders, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
A. T. Phan
Department of Gastrointestinal Medical Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
R. L. Bassett Jr. Department of Biostatistics, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
Results Included in the analysis were 106 patients with 180 PET/CT scans. Of the 106 patients, 7 underwent PET/CT only for initial staging, 84 underwent PET/CT only for restaging, and 15 underwent PET/CT for both initial staging and restaging. PET/CT changed the management plan in 1 of 22 patients (5 %) at initial staging and 9 of 99 patients (9 %) at restaging. In 5 of the patients in whom PET/CT changed the management plan, PET/CT showed response to chemotherapy but contrast-enhanced CT showed stable disease. Sensitivity, specificity, and accuracy were 100 %, 100 %, and 100 % for PET/CT at initial staging; 92.6 %, 100 %, and 96.4 % for CT at initial staging; 98.4 %, 100 %, and 99.5 % for PET/CT at restaging; and 96.8 %, 98.6 %, and 98.0 % for CT at restaging, respectively. No PET/CT parameters were associated with survival at either initial diagnosis or recurrence.
Conclusion PET/CT findings could substantially change the management plan in a small proportion of patients with ACC. Although lesion detection was similar between PET/CT and CT, PET/CT may be preferred for chemotherapeutic response assessment because it may predict response before anatomic changes are detected on CT.
Keywords PET/CT . Adrenocortical carcinoma . Impact on management · Response assessment
Introduction
Adrenocortical carcinoma (ACC) is a rare and aggressive malignancy with high rates of morbidity and mortality. The reported incidence is approximately 2 cases per 1 million individuals per year [1]. At present, standard therapy for ACC is complete surgical resection plus adjuvant mitotane in patients with resectable disease and combination chemo- therapy in patients with unresectable or metastatic disease [2-5]. ACC has a high recurrence rate after surgical resection.
Patients with ACC require repeated body imaging for detec- tion of recurrence and assessment of response to therapy. In most patients, CT or MRI of the chest, abdomen, and pelvis is done every 3 months during the first 2 years after complete resection to monitor for recurrence and on average every 2 - 3 months in patients with metastatic disease to assess response to chemotherapy [16]. Additionally, 18F-FDG PET has been used for surveillance and evaluation of response to therapy. During the past decade, combined PET/CT has also been used for imaging in various malignancies. However, the literature on PET and PET/CT in ACC is limited to case reports and small case series [7-10].
We evaluated the impact of PET/CT on the management of ACC by comparing management plans based on PET/CT with management plans based on conventional contrast-enhanced CT.
Materials and methods
Patients
This study was approved by our institution’s Institutional Review Board, which waived the requirement for informed consent, and was performed in compliance with the Health Insurance Portability and Accountability Act. We searched our institution’s tumor registry to identify all patients who were referred to our institution for treatment of ACC during the period from January 2002 through October 2012. A total of 400 patients met these criteria. We then reviewed the records of those 400 patients to identify patients who had undergone PET/CT during their disease course, and we iden- tified 144 patients. Of these 144 patients, 38 were excluded because they visited our institution only once to obtain a second opinion (26), had PET only (8), or had a history of another malignancy (4). The remaining 106 patients were included. In all patients, the pathological diagnosis of ACC was confirmed at our institution as part of our standard prac- tice. Patient information was obtained by direct chart review. Disease stage was determined according to the European Network for the Study of Adrenal Tumors staging system [11]. Patient characteristics are summarized in Table 1. Pa- tients were categorized into three groups: patients who underwent PET/CT for initial staging only, patients who underwent PET/CT for both initial staging and restaging, and patients who underwent PET/CT for restaging only.
PET/CT and CT imaging
For 18F-FDG PET/CT, patients fasted for 6 h before 18F-FDG administration to achieve a blood glucose level of less than 120 mg/dL. 18F-FDG (185 - 370 MBq per injection) was administered intravenously. Approximately 60 min later, an
| Characteristic Timing of PET/CT | ||||
|---|---|---|---|---|
| Initial staging only (n=7) | Initial staging and restaging (n=15) | Restaging only (n=84) | ||
| Gender (n) | ||||
| Male | 3 | 8 | 27 | |
| Female | 4 | 7 | 57 | |
| Age at diagnosis (years) | ||||
| Median | 58 | 51 | 47 | |
| Range | 40 - 65 | 21 - 77 | 3 - 76 | |
| Follow-up time (months) | ||||
| Median | 7.0 | 21.4 | 33.2 | |
| Range | 1.5 - 75.8 | 6.0 - 51.7 | 5.0 - 283.4 | |
| Race/ethnicity (n) | ||||
| White | 7 | 14 | 71 | |
| Latino | 0 | 1 | 4 | |
| African American 0 | 0 | 5 | ||
| Asian | 0 | 0 | 4 | |
| Initial stage (ENSAT 2008) (n) | ||||
| I | 0 | 0 | 3 | |
| II | 0 | 2 | 25 | |
| III | 2 | 3 | 50 | |
| IV | 5 | 10 | 6 | |
ENSAT European Network for the Study of Adrenal Tumors
integrated PET/CT system (Discovery ST, STe, or RX; GE Healthcare) was used to acquire imaging data. CT was per- formed concomitantly with each PET acquisition for anatomic localization and attenuation correction; parameters included 3.75-mm axial slice placement, 140 kV, and 120 mA at a 13.5- mm table speed. PET was performed in 2-dimensional or 3- dimensional mode at 3 - 5 min per bed station. PET, CT, and fusion images were displayed in 3.75-mm slices. Attenuation- corrected and non-attenuation-corrected datasets were recon- structed. Conventional contrast-enhanced CT was performed with a LightSpeed or HiSpeed Advantage helical scanner (GE Medical Systems). Scanning was started 60 s after the start of administration of 150 mL of 60 % nonionic contrast agent (Optiray 320; Mallinckrodt Inc.) at a rate of 3 mL/s.
If imaging was performed at an outside institution, avail- able raw imaging data were obtained from that institution. The timing of imaging studies was at the primary physician’s discretion. PET/CT and contrast-enhanced CT had to be per- formed within 30 days of one another.
Image review and tumor analysis
Imaging data were reviewed by experienced nuclear medicine physicians and radiologists at our institution. The highest metabolic activity within the tumor (maximum standard
uptake value; SUVmax) and total lesion glycolysis (TLG) were measured using an Advantage workstation (GE Healthcare). SUV was defined as measured activity concentration (becquerels per gram) multiplied by body weight (grams) divided by injected activity (becquerels). TLG was defined as average metabolic activity within the tumor multiplied by tumor volume, with a threshold of 45 % SUVmax in the volume of interest [12].
Impact of PET/CT on management plans
The situations in which PET/CT was classified as having an impact on management plan and the specific impact associat- ed with each situation were as follows:
· PET/CT identified an FDG-avid lesion not seen on CT: management changed from surgery to chemotherapy or from observation to surgery.
· Lesions visible on CT but FDG avidity absent or very low on PET/CT: management changed from chemotherapy to local therapy or observation.
· PET/CT identified an FDG-avid lesion not seen on CT that could be treated with local therapy: local therapy added to ongoing chemotherapy.
Sensitivity, specificity, and accuracy of imaging
Sensitivity, specificity, and accuracy were calculated at initial diagnosis and recurrence. PET/CT and CT findings were classified as follows:
· True-positive: lesions visualized on imaging corresponded with histopathologically detected lesions or with follow- up imaging findings of progression within 6 months.
· False-positive: lesions visualized on imaging did not cor- respond with histopathologically detected lesions or re- solved on subsequent follow-up imaging without any treatment.
· True-negative: imaging and subsequent imaging over a period of at least 6 months showed no evidence of disease.
· False-negative: imaging showed no evidence of disease but either subsequent imaging studies or subsequent his- topathological examination showed disease within 3 months.
For patients with multiple metachronous recurrences, all recurrences were considered. The sensitivity, specificity, and accuracy of PET/CT and CT were calculated using region-by- region comparison. Each scan was divided into five regions: adrenal bed, liver, abdomen, chest, and bone. Each region was rated as positive or negative.
Outcomes in PET/CT chemoresponders and nonresponders
For patients treated with mitotane, combination chemothera- py, or both, chemoresponders and nonresponders by PET/CT were compared for progression-free survival (PFS) and over- all survival (OS). Patients included in this analysis underwent PET/CT both before and during chemotherapy. The interval between two PET/CT scans had to be 6 months or less. A metabolic response on PET/CT was defined as a decline in SUV max of more than 25 % after chemotherapy, in accordance with the European Organization for Research and Treatment of Cancer response criteria [13]. Target lesions on PET/CT were defined as all FDG-avid lesions up to a maximum of five lesions total and a maximum of two lesions per organ. The Response Evaluation Criteria in Solid Tumors were used in CT evaluation [14]. Target lesions on CT were defined as all lesions up to a maximum of five lesions total and a maximum of two lesions per organ.
Statistical analysis
Statistical analyses were performed with R version 3.0.1 [15]. Differences in sensitivity between PET/CT and CT were com- pared with the McNemar test. PFS was calculated for patients treated with chemotherapy and defined as the time from the beginning date of treatment to tumor progression. OS was defined as the time from the date of initial treatment to death from any cause or last follow-up. The Kaplan-Meier method and a log-rank test were used to compare PFS and OS at both initial diagnosis and recurrence stratified by various potential prognostic factors. A Cox proportional hazards regression model was used for multivariate analysis. P<0.05 was con- sidered statistically significant.
Results
PET/CT scans at initial staging and restaging
Median follow-up time after initial PET/CT was 33.2 months (range 1 - 283 months). Seven patients underwent PET/CT for initial staging only, 15 underwent PET/CT for both initial staging and restaging, and 84 underwent PET/CT for restaging only. Among the 99 patients who underwent PET/ CT for restaging, 21 were restaged after chemotherapy, and 78 were restaged after surgery. Among the 22 patients with PET/ CT for initial staging, none had stage I disease and 15 (68 %) had stage IV disease at initial staging. A total 313 PET/CT scans were performed, and of these, 180 with corresponding conventional contrast-enhanced CT scans were analyzed: 7 scans in patients who had PET/CT for initial staging only, 39
scans in patients who had PET/CT for both initial staging and restaging (15 at initial diagnosis, 24 at restaging), and 134 scans in patients who had PET/CT for restaging only. Three PET/CT scans in patients with PET/CT for initial staging only, and 24 PET/CT scans in patients with PET/CT for restaging only were performed at outside institutions and were included in the study.
Impact of PET/CT on management plans
The impact of PET/CT on management plans is summarized in Table 2. The median interval between PET/CT and CT was 5 days (range 0- 30 days). Among the 22 patients with PET/ CT at initial diagnosis, 1 patient (5 %) had the management plan at initial diagnosis changed by PET/CT. Among the 99 patients with PET/CT at restaging, 9 patients (9 %) had the management plan at restaging changed by PET/CT. Images from two patients with management plans changed by PET/ CT are shown in Figs. 1 and 2. Details of the ten cases in which PET/CT had an impact are provided in Table 3. In five of the cases in which PET/CT changed the management plan, PET/CT showed a metabolic response to chemotherapy while contrast-enhanced CT showed stable disease. In these patients, PET/CT showed response before response was evident on contrast-enhanced CT.
| Pre-PET/CT management plan | Post-PET/CT management plan | No. of patients |
|---|---|---|
| PET/CT at initial diagnosis | ||
| Surgery | Chemotherapy | 1ª |
| Surgery | Surgery | 4 |
| Chemotherapy | Chemotherapy | 17 |
| PET/CT at restaging | ||
| Chemotherapy | Surgery | 5ª |
| Chemotherapy | Embolization | 1ª |
| Chemotherapy | Observation | 1ª |
| Observation | Surgery | 1ª |
| Chemotherapy | Chemotherapy+palliative radiotherapy | 1ª |
| Surgery | Surgery | 7 |
| Surgery+radiofrequency ablation | Surgery+radiofrequency ablation | 1 |
| Chemotherapy | Chemotherapy | 72 |
| Observation | Observation | 13 |
| Best supportive care | Best supportive care | 4 |
| Chemoradiotherapy | Chemoradiotherapy | 1 |
| Chemotherapy +palliative radiotherapy | Chemotherapy+palliative radiotherapy | 1 |
a PET/CT changed management
Sensitivity, specificity, and accuracy
The performance of PET/CT and CT in the detection of disease is summarized in Table 4. In 22 patients PET/CT was preformed for initial staging. Of the 110 regions checked in these patients, 32 (29 %) contained histopathologically confirmed disease. In addition to the primary tumor in the adrenal bed in all 22 patients, there were ten regions with metastases including five liver regions, four lung regions, and one bone region. An additional 22 regions had true-positive findings based on follow-up imaging findings of progression within 6 months. Those were ten chest regions, seven liver regions, three abdominal regions, and two bone regions. Sen- sitivity, specificity, and accuracy were 100 %, 100 %, and 100 %, respectively, for PET/CT and 92.6 %, 100 %, and 96.4 %, respectively, for CT. There were four regions with false-negative findings on CT: CT missed disease in three bone regions (rib, acetabulum, and spine) and one neck lymph node. Sensitivity did not differ significantly between PET/CT and CT (P=0.13).
Recurrence was identified in 75 patients. Of these patients, 41 had evaluation for recurrence with both PET/CT and CT. Of the 205 regions checked in these patients, 18 (9 %) contained histopathologically confirmed disease. In addition to the recurrent tumors in the adrenal bed in 12 patients, there were six regions with metastases including four liver regions and two chest regions. An additional 44 regions had true- positive findings based on follow-up imaging findings of progression within 6 months. Those were 17 chest regions, 15 abdominal regions, 6 liver regions, 4 adrenal bed regions, and 2 bone regions. Sensitivity, specificity, and accuracy were 98.4 %, 100 %, and 99.5 %, respectively, for PET/CT, and 96.8 %, 98.6 %, and 98.0 %, respectively, for CT. There was one region with a false-negative finding on PET/CT. In this patient, CT detected a metastatic lesion in the liver that did not show FDG uptake. The lesion had grown on subsequent imaging. Similarly, there were two regions with false- negative findings on CT. There were also two regions with false-positive findings on CT; in both cases, the regions were confirmed pathologically to be free of disease. There was no significant difference in sensitivity between PET/CT and CT (P=0.20).
Clinical outcomes in PET/CT chemoresponders and nonresponders
Of 18 patients treated with chemotherapy as an initial therapy, 8 were treated with mitotane plus combination chemotherapy, 6 were treated with mitotane only, and 4 were treated with combination chemotherapy . Of these 18 patients, 12 were evaluated with PET/CT both before and after chemotherapy. The median interval between PET/CT scans was 2.8 months (range 2.1 - 5.9 months). Of these patients, 5 were PET/CT
a
C
7
b
d
responders. The mean decline in SUVmax in PET/CT re- sponders was 68.9 % (range 41.7 - 75.7 %). There was no significant difference between responders and nonresponders in median PFS (7.3 and 7.2 months, respectively; P=0.46) or OS (20.2 and 11.9 months, respectively; P=0.45). However, three of the five responders were able to proceed to local therapy after chemotherapy based on PET/CT findings.
Of 20 patients treated with chemotherapy for recurrence, 12 were treated with mitotane only, 5 were treated with mitotane plus combination chemotherapy, and 3 were treated in a clin- ical trial. The median interval between PET/CT scans was 2.6 months (range 0.9 - 0.0 months). Of these patients, 6 were PET/CT responders. The mean decline in SUV max in PET/CT responders was 74.8 % (range 34.8 - 100 %). There was no significant difference between responders and nonresponders in median PFS (5.3 and 5.9 months, respectively; P=0.31) or OS (20.0 and 30.2 months, respectively; P=0.35).
Prognostic factors
Of the 22 patients with PET/CT for initial staging, 18 were treated with chemotherapy as an initial therapy.
The analysis of prognostic factors was limited to these patients. The median SUVmax and TLG for primary lesions were 13.8 (range 3.3 - 37.5) and 188.6 (range 81.2 - 1333.1), respectively. In univariate analysis of predictors of survival at initial diagnosis, neither dichot- omized SUVmax (SUVmax cut-off: 10) nor TLG (TLG cut-off 200) of the primary lesion was associated with PFS or OS. Multivariate analysis of survival predictors at initial diagnosis could not be performed because of the small number of events.
Of the 99 patients with PET/CT for restaging, 31 had PET/CT performed at first recurrence. The analysis of prognostic factors was limited to these patients. The median SUVmax and TLG for recurrent lesions were 8.4 (range 2.2 - 43.6) and 76.5 (range 11.5 - 513.5), respectively. In univariate analysis of predictors of sur- vival at recurrence, neither dichotomized SUVmax nor TLG (same cut-off values as above) of the recurrent lesion was associated with PFS or OS. Multivariate analysis showed that SUVmax greater than 10 was not an independent poor prognostic factor (hazard ratio 1.27, 95 % confidence interval 0.48 - 3.36; P=0.63).
a
b
Although we explored other potential cut-off values for SUVmax and TLG, no significant association with PFS or OS was noted at either initial diagnosis or recurrence.
Discussion
We found that PET/CT resulted in a change in clinical man- agement plan in about 5 % of patients at initial staging and 9 % of patients at restaging compared with contrast-enhanced CT. PET/CT was more useful than CT for assessing response to chemotherapy in a small proportion of patients. We also found that sensitivity, specificity, and accuracy were similar for PET/ CT and contrast-enhanced CT at both initial staging and recurrence.
On the basis of an analysis of data from the National Oncologic PET Registry, opened in 2006, Hillner et al. re- ported that 40.4 % of 1,564 PET scans at initial diagnosis and 33.2 % of 1,478 PET scans at restaging had an impact on intended management for “all other” malignancies [17]. Con- sidering that the rates of impact on the management plan were 5 % at initial diagnosis and 9 % at restaging in our study, compared to 30- 40 % for other cancer types in the study by Hillner et al., it seems that PET/CT showed less impact on the management plan in patients with ACC than in patients with other malignancies. This discrepancy may have been due to selection bias, as many patients were referred to our institution with advanced or recurrent disease.
The sensitivity, specificity, and accuracy of PET/CT in ACC were unknown until recently. Deandreis et al. analyzed nine articles to calculate the sensitivity and specificity. Al- though their report included only 51 patients with ACC among 549 patients with adrenal masses, the authors reported that the sensitivity of PET/CT in the detection of ACC was 89 - 100 % and the specificity 70 - 100 % [18]. Because not all lesions in our present study were evaluated histopatholog- ically, we had to define follow-up imaging findings as the standard of reference in some cases. However, our results showed that PET/CT was similar to or possibly slightly supe- rior to CT in terms of diagnostic discrimination. Mackie et al. showed that PET/CT could be a good tool for restaging in patients with resected ACC [9]. However, they analyzed only 12 patients and did not compare PET/CT findings with CT findings as we did in the present study. Hence, it is difficult to compare our results with theirs. Leboulleux et al. found that there was no significant difference in recurrence detection between PET/CT and CT [8], which is consistent with our results.
We found that SUV max, TLG, and decline in SUV max after chemotherapy did not correlate with clinical outcome either at initial diagnosis or at recurrence. Recently, Tessonnier et al. found in a retrospective study of 37 patients with ACC that FDG uptake at initial diagnosis did not correlate with disease- free survival or OS, which agrees with our findings [19]. On the other hand, Leboulleux et al. found in 21 patients that SUVmax greater than 10 at recurrence was significantly asso- ciated with poorer survival [8]. However, because ACC is rare, the number of patients included in each study was small, which may account for the differences in findings. Addition- ally, some patients in our present study were treated with multidisciplinary treatment, and thus treatment differences might also have affected the results. Further prospective stud- ies with appropriate numbers of patients are necessary to verify whether SUVmax, TLG, and decline in SUVmax are prognostic factors in patients with ACC.
We also found that PET/CT demonstrated response to chemotherapy earlier than CT did. Ten patients had the man- agement plan affected by PET/CT. Among these patients,
| Patient no. | Timing of PET/CT | Pre-PET/CT management plan | Post-PET/CT management plan | Findings | |
|---|---|---|---|---|---|
| CT | PET/CT | ||||
| 1 | Initial diagnosis | Surgery | Chemotherapy | False negative (neck) | Positive |
| 2 | Restaging | Chemotherapy | Surgery | PR | PMR |
| 3 | Restaging (shown in Fig. 1) | Chemotherapy | Surgery | SD | PMR |
| 4 | Restaging | Chemotherapy | Embolization | SD | PMR |
| 5 | Restaging | Chemotherapy | Surgery | SD | PMR |
| 6 | Restaging | Chemotherapy | Surgery | SD | PMR |
| 7 | Restaging | Chemotherapy | Surgery | SD | PMR |
| 8 | Restaging | Chemotherapy | Observation | PD | PET/CT and biopsy were negative |
| 9 | Restaging (shown in Fig. 2) | Observation | Surgery | SD | PMD (liver) |
| 10 | Restaging | Chemotherapy | Chemotherapy+palliative radiotherapy | SD | PMD (bone) |
PR partial response, SD stable disease, PMR partial metabolic response, PMD progressive metabolic disease
PET/CT predicted chemotherapeutic response in six. These six patients went on to local therapy on the basis of PET/CT findings. One of these patients had disease considered stage IV at diagnosis and was previously reported in a case report on the potential usefulness of PET/CT in ACC [16]. At the time of writing, this patient was alive more than 4 years after surgery. These results mean that PET/CT may be useful to select the optimal treatment in patients with advanced disease who need multidisciplinary treatment.
Our results also suggest criteria for appropriate use of PET/ CT in daily practice in patients with ACC, a topic not specif- ically addressed in either the European Society for Medical Oncology guideline for adrenal cancer [20] or a recently published review [2]. If a patient with advanced ACC has
| Parameter | Initial staging (110 regions) | Recurrence (205 regions) | ||
|---|---|---|---|---|
| PET/CT | CT | PET/CT | CT | |
| True-positive (n) | 54 | 50 | 62 | 60 |
| True-negative (n) | 56 | 56 | 142 | 141 |
| False-positive (n) | 0 | 0 | 0 | 2 |
| False-negative (n) | 0 | 4 | 1 | 2 |
| Sensitivity (%) | 100 | 92.6 | 98.4 | 96.8 |
| 95 % CI | 94.6 - 100 | 82.1 - 97.9 | 91.5-100 | 88.8 -99.6 |
| Specificity (%) | 100 | 100 | 100 | 98.6 |
| 95 % CI | 94.8 - 100 | 94.8 - 100 | 97.9 - 100 | 95.0 - 99.8 |
| Accuracy (%) | 100 | 96.4 | 99.5 | 98.0 |
| 95 % CI | 97.3 - 100 | 91.0 - 99.0 | 97.3 - 100 | 95.1 -99.5 |
the potential to proceed to surgical resection, sequential PET/ CT would give additional information on the basis of which the optimal management plan can be chosen. On the other hand, routine PET/CT might not be necessary for restaging given that the performance of PET/CT was similar to that of CT at recurrence. Proper timing of PET/CT might be particu- larly important in terms of cost-effectiveness and accurate management. Additionally, PET/CT would be useful in pa- tients with impaired renal function, in whom intravenous contrast material for contrast-enhanced CT can lead to kidney damage. In such cases, PET/CT may be an alternative to CT.
Our study had several potential limitations. First, this was a single-center retrospective study. Second, we might have overestimated the performance of PET/CT or CT because these scans were not performed sequentially and readers were not blinded to the findings of the other study. Third, PET/CT was not performed at regular intervals in all patients. Fourth, and the biggest limitation, about two-thirds of the patients who underwent PET/CT for initial staging had stage IV dis- ease at diagnosis. Such a selection bias might have limited our assessment of the role of PET/CT at initial diagnosis. The strengths of our study lie in the number of patients included and the fact that this is the first comprehensive report to demonstrate the usefulness of PET/CT in ACC.
Conclusion
PET/CT findings could substantially change the management plan in a small proportion of patients with ACC. Although lesion detection was similar between contrast-enhanced CT and PET/CT, PET/CT may be preferred for chemotherapeutic response assessment because it may predict response earlier than the detection of anatomic changes on CT.
Acknowledgments We thank the staff at MD Anderson Cancer Center for their assistance and especially Ms. Richelle D. Millican, Supervisor, Diagnostic Imaging, for data collection. This report was edited by Stephanie Deming in MD Anderson’s Department of Scientific Publications.
This work was supported in part by the MD Anderson Cancer Center James E. Anderson Distinguished Professorship in Nuclear Medicine (to Dr. Macapinlac), the Society of Nuclear Medicine and Molecular Imaging 2012/2014 Wagner-Torizuka Fellowship (to Dr. Takeuchi), and the NIH/ NCI under award number P30CA016672.
Conflicts of interest None.
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