Diagnostic and prognostic value of 18F-FDG PET/CT in recurrent germinal tumor carcinoma

The aim of this bicentric retrospective study was to assess the diagnostic performance, the prognostic value, the incremental prognostic value and the impact on therapeutic management of ¹⁸F-FDG PET/CT in patients with suspected recurrent germinal cell testicular carcinoma (GCT).

From the databases of two centers including 31,500 ¹⁸F-FDG PET/CT oncological studies, 114 patients affected by GCT were evaluated in a retrospective study. All 114 patients underwent ¹⁸F-FDG PET/CT for suspected recurrent disease. Diagnostic performance of visually interpreted ¹⁸F-FDG PET/CT and potential impact on the treatment decision were assessed using histology (17 patients), other diagnostic imaging modalities (i.e., contrast enhanced CT in 89 patients and MRI in 15) and clinical follow-up (114 patients) as reference. Progression-free survival (PFS) and overall survival (OS) rates were computed by means of Kaplan-Meier survival analysis. The progression rate (Hazard Ratio-HR) was determined using univariate Cox regression analysis by considering various clinical variables.

Recurrent GCT was confirmed in 47 of 52 patients with pathological ¹⁸F-FDG PET/CT findings, by means of histology in 18 patients and by other diagnostic imaging modalities/follow-up in 29. Sensitivity, specificity, accuracy, positive and negative likelihood ratio (LR+ and LR-, respectively), pre-test Odds-ratio and post-test Odds-ratio of ¹⁸FDG PET/CT were 86.8%, 90.2%, 88.4%, 8.85, 0.14, 0.85, 8.85, respectively.¹⁸F-FDG PET/CT impacted significantly on therapeutic management in 26/114 (23%) cases (from palliative to curative in 12 patients, from “wait and watch” to new chemotherapy in six patients and the “wait-and-watch” approach in eight patients with unremarkable findings). At 2 and 5-year follow-up, PFS was significantly longer in patients with a negative than a pathological ¹⁸F-FDG PET/CT scan (98% and 95% vs 48% and 38%, respectively; p = 0.02). An unremarkable scan was associated also with a longer OS (98% after 2 years and 95% after 5 years, p = 0.02). At univariate Cox regression analysis, a pathological ¹⁸F-FDG PET/CT scan was associated with an increased risk of disease progression (HR = 24.3, CI 95% 14.1-40.6; p = 0.03) and lower OS (HR = 17.3 CI 95% 4,9-77; p < 0.001). Its prognostic value was confirmed also if tested against advanced disease at diagnosis and rising Human Chorionic Gonadotropin Beta (HCGB) or Alpha-Fetoprotein (AFP) (HR = 7.3 for STAGE III-PET+, p = 0.03; HR = 14.3 elevated HCGB-PET+, p = 0.02; HR 10.7 elevated AFP-PET+, p = 0.01) At multivariate analysis, only a pathological ¹⁸F-FDG PET/CT scan and advanced disease in terms of TNM staging were predictors of disease progression and OS. ¹⁸F-FDG PET/CT showed incremental value over other variables both in predicting PFS (chi-square from 24 to 40, p < 0.001) and OS (chi-square from 32 to 38, p = 0.003).

¹⁸F-FDG PET/CT has a very good diagnostic performance in patients with suspected recurrent GCT and has an important prognostic value in assessing the rate of PFS and OS. Furthermore, ¹⁸F-FDG PET/CT impacted the therapeutic regimen in 23% of patients, thus providing a significant impact in the restaging process.