False-positive fluorodeoxyglucose positron emission tomography results after chemotherapy in patients with metastatic seminoma.

Introduction: The treatment of residual masses after chemotherapy in seminomas remains a controversial topic. Postchemotherapy retroperitoneal lymph node dissection (PC-RPLND) in all patients would lead to severe overtreatment with a high rate of complications and additional procedures. For this reason, fluorodeoxyglucose positron emission tomography (FDG-PET) was introduced. FDG-PET has an accuracy of 88%. In 15% of cases, FDG-PET findings are false positive (FP) with unclear consequences. Therefore, we retrospectively investigated the rate of unnecessary procedures due to FP results on FDG-PET.

Materials And Methods: Between July 2003 and September 2013 we performed 305 PC-RPLNDs in 277 patients, 22 because of metastatic seminoma. Of them, 11 patients had a preoperative FDG-PET at least 6 weeks after chemotherapy. Indication for surgery was a marker-negative progression of the lesion in 7 patients who did not undergo FDG-PET, a marker-negative progression with a negative result on FDG-PET in 2 patients, and a positive result on FDG-PET with normal markers in 9 patients. Furthermore, PC-RPLND was indicated in 3 patients because of ureteral compression/infiltration with ureteral stents or nephrostomies. In 1 patient, there was uncertainty whether the initial retroperitoneal tumor contained choriocarcinoma elements. Standardized uptake values (SUVs) were recorded for all patients undergoing FDG-PET.

Results: The FDG-PET findings were FP in 7 of 11 (64%) patients. The median age of the patients was 45.4 years (39-49). The median SUV in the patients was 6.6 (3.1-11.6), and the median diameter of the residual mass was 6.8 cm (2.9-11). In 4 of 7 patients, intraoperative or postoperative complications occurred (polar artery ligation with functional loss, bilateral non-nerve-sparing technique with retrograde ejaculation, ureteral replacement with an ileal segment, and pulmonary embolism).

Conclusion: In patients with metastatic seminoma who received chemotherapy, FDG-PET is a valuable tool to evaluate whether the residual mass contains viable tumor tissue or only necrosis. Nevertheless, because of FP results, a subgroup is overtreated with consecutive mortality or morbidity. We suggest an alternative therapy algorithm. In case of a positive result on FDG-PET studies, at least 8 weeks after the end of the chemotherapy, only a minority require surgery (e.g., patients with ureteral compression, patients with high risk of recurrence, or patients with unclear initial histology). In all other cases, we suggest a repeat FDG-PET study at least 6 weeks after the initial PET scan. Only in cases of increased SUVs or progressive disease histology should be obtained, all others can be on active surveillance.