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

Abstract

IntroductionThe 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 methodsBetween 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. ResultsThe 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 6.8cm (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). ConclusionIn 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.