Incidence and risk factors for contralateral testicular tumor

419

Background: Patients with testicular germ cell tumor (TGCT) are at increased risk of developing a metachronous contralateral testicular tumor (CLTT). It is unclear whether the histology of the primary tumor and treatment with platinum-based chemotherapy are associated with the risk of CLTT. The primary aim of this study was to analyze the association between number of chemotherapy cycles and risk of CLTT. Methods: We evaluated the incidence of metachronous CLTT (≥2 months after diagnosis of primary TGCT) in a nationwide cohort consisting of patients diagnosed with TGCT between 1989 and 2007. Standardized incidence ratios (SIRs) were computed to compare CLTT incidence with TGCT in the general population and the cumulative incidence of CLTT was estimated. We analyzed the association between treatment with chemotherapy and risk of CLTT in a multivariate Cox-model. Results: The entire cohort consisted of 4,755 patients (seminoma: n=2,612; 54.9%, nonseminomatous germ cell tumor [NSGCT]: n=2,143; 45.1%). The median age at diagnosis was 33 years (IQR 26-40). A total of 1,047 patients (22.0%) were treated with platinum-based chemotherapy for their primary TGCT (seminoma: n=189, NSGCT: n=858). Median follow-up was 17.0 years (IQR 12.7-22.0). A CLTT was diagnosed in 136 patients. The median interval to CLTT diagnosis was 6.1 years (range 0.8-19.7). The overall 20-year cumulative incidence was 3.4% (95% CI 2.8-4.0) and was higher after seminoma (4.0%; 95% CI 3.3-4.9), compared to NSGCT (2.6%; 95% CI 1.9-3.4). The SIRs were for seminoma: 22.1 (95% CI 17.8-27.1), for NSGCT: 8.6 (95% CI 6.3-11.6) and for the entire cohort: 14.6 (95% CI 12.2-17.2). In multivariate analysis, the risk of developing a CLTT decreased with age (HR 0.93; 95% CI 0.90-0.96), was lower after NSGCT (HR 0.58; 95% CI 0.35-0.96), and decreased with every additional cycle of chemotherapy (HR 0.74; 0.64-0.85). This corresponds to a 26% lower risk of CLTT per extra chemotherapy cycle. Conclusions: TGCT patients have an almost 15 times higher risk of developing a CLTT, compared to the general population. The risk is 2 times higher after a seminoma, compared to NSGCT, and decreases with every additional cycle of chemotherapy. Especially in high risk patients, lifelong self-examination is advised.