18F-FDG PET/CT value in the detection of seminoma and correlation with CT and tumor marker levels - up to 8 years of follow-up.

Abstract

Positron emission tomography/computed tomography using fluorine-18 fluoro-deoxyglucose (18F-FDG PET/CT) is not routinely used for diagnosis of testicular carcinoma. Unlike CT which cannot confirm with certainty the nature of the lesions, especially in post-therapy setting, 18F-FDG PET/CT detects active disease by showing increased glucose metabolism within the lesions. Determination of 18F-FDG PET/CT usefulness in detection of seminoma, therapy response evaluation and comparison to CT findings and tumor marker levels. Eighty-two men (age 39.8±10.1) after orchiectomy and histopathological confirmation of seminoma were included in this study. Indications for 18F-FDG PET/CT were initial staging, restaging after chemo/radiotherapy with positive/uncertain CT, suspected recurrence on CT, elevated tumor markers. All patients had clinical follow-up of up to 8 years (median 33.5) after the first 18F-FDG PET/CT examination. Degree of metabolic activity was analyzed visually and semi-quantitatively using maximum standardized uptake value(SUVmax). Fluorine-18-FDG PET/CT was true positive in 36 patients (43.9%) with average SUVmax of 7.9±4.8.Recurrence was mostly found in retroperitoneal lymph nodes and distant metastases in lungs, bones, liver. Six findings were false positive and 3 false negative. Sensitivity, specificity, accuracy of 18F-FDG PET/CT were 92.3%, 86.0%, 89.0% and of CT 60.8%, 66.6%, 63.4%. Pearson Chi-square test showed statistically significant difference between the results of 18F-FDG PET/CT and CT (P=0.016). Significant correlation was found between positive 18F-FDG PET/CT findings and levels of LDH (P=0.043), while non-significant between AFP, β-hCG (P>0.05). Fluorine-18-FDG PET/CT was superior to CT in evaluation of therapy response, active disease in residual tissue and normal size lymph nodes, as well as when CT was negative and tumor markers were elevated. Elevated lactate dehydrogenase (LDH) contributes to positive 18F-FDG PET/CT findings.