Positron emission tomography scans in the evaluation of postchemotherapy residual masses in patients with seminoma

Purpose: To assess the ability of positron emission tomography (PET) scans in differentiating between necrosis and viable seminoma in postchemotherapy (PC) residual disease. Patients and Methods: We conducted a prospective study of 29 patients with seminoma at Indiana University. All patients had PC residual disease. Computed tomography and PET scans were performed for 19 patients after primary chemotherapy (group A) and for 10 patients after salvage chemotherapy (group B). Results: In group A, the PC masses were ≥ 3 cm in 14 patients, less than 3 cm in three patients, and not quantified in two patients. All of the patients in group A had negative PET scan results and have had stable or decreasing residual mass size (median follow-up duration, 11.5 months; range, 6 to 26 months). In group B, the PC masses were ≥ 3 cm in four patients, less than 3 cm in five patients, and not quantified in one patient. One patient had a positive PET scan result for a posterior mediastinal mass. Pathologic diagnosis of the PET-positive mass showed only necrotic tissue. The same patient had a negative PET scan of the retroperitoneal mass but relapsed in that area. Overall, of patients in group B, five have stable or decreasing mass (median follow-up duration, 8 months; range, 7 to 22 months), and five had relapsed disease. Conclusion: PET scans have no apparent benefit in PC evaluation of residual masses in bulky seminoma.