18F-FDG PET/CT for primary staging of patients with testicular germ cell tumors: the predictors of 18F-FDG PET positivity and prognostic value of PET derived metabolic parameters.

Purpose: The aim of this study was to investigate the role of histopathologic and biochemical parameters for predicting F-FDG PET positivity for primary staging in patients with newly diagnosed testicular germ cell tumors (TGCT). It was also aimed to evaluate the prognostic value of PET derived metabolic features in this patient group.

Materials And Methods: The imaging findings of 51 patients who were diagnosed as TGCT and underwent F-FDG PET/CT for primary staging after surgery between 2009 and 2019 were evaluated retrospectively. In terms of the presence of F-FDG uptake consistent with metastasis, the patients were divided into two groups as 'PET-positive' and 'PET-negative'. In 'PET-positive' patients, highest maximum standardized uptake values of metastatic lesions, whole-body total metabolic tumor volumes (wb-TMTV) and total lesion glycolysis (wb-TLG) were extracted. Pathological tumor types, pathological T stages (pT), tumor marker (TM) levels (AFP, hCG, LDH) after orchiectomy and overall survival (OS) times in months were also recorded. The predictive value of variables for OS was evaluated using the Kaplan-Meier survival analysis.

Results: PET positivity was observed in 28% of pT1 and in 83.3% in pT2-T3 tumors (P < 0.001). In the logistic regression analysis to predict 'PET positivity', pT stage and ≥2 elevated TMs were found as independent significant predictors. Survival analysis demonstrated that wb-TMTV, wb-TLG and TMs were significantly associated with prognosis for OS.

Conclusion: The likelihood of PET positivity was significantly higher in patients with elevated TMs and pT2-T3 stages compared to those with normal TMs and pT1 tumors. PET derived quantitative metabolic-volumetric parameters can be used as biomarkers to identify patients with poor prognosis in TGCT.