RESUMEN
BACKGROUND: Testicular germ cell tumour (TGCT) patients are at increased risk of developing a contralateral testicular germ cell tumour (CTGCT). It is unclear whether TGCT treatment affects CTGCT risk. METHODS: The risk of developing a metachronous CTGCT (a CTGCT diagnosed ≥6 months after a primary TGCT) and its impact on patient's prognosis was assessed in a nationwide cohort comprising 3749 TGCT patients treated in the Netherlands during 1965-1995. Standardised incidence ratios (SIRs), comparing CTGCT incidence with TGCT incidence in the general population, and cumulative CTGCT incidence were estimated and CTGCT risk factors assessed, accounting for competing risks. RESULTS: Median follow-up was 18.5 years. Seventy-seven metachronous CTGCTs were diagnosed. The SIR for metachronous CTGCTs was 17.6 (95% confidence interval (95% CI) 13.9-22.0). Standardised incidence ratios remained elevated for up to 20 years, while the 20-year cumulative incidence was 2.2% (95% CI 1.8-2.8%). Platinum-based chemotherapy was associated with a lower CTGCT risk among non-seminoma patients (hazard ratio 0.37, 95% CI 0.18-0.72). The CTGCT patients had a 2.3-fold (95% CI 1.3-4.1) increased risk to develop a subsequent non-TGCT cancer and, consequently, a 1.8-fold (95% CI 1.1-2.9) higher risk of death than patients without a CTGCT. CONCLUSION: The TGCT patients remain at increased risk of a CTGCT for up to 20 years. Treatment with platinum-based chemotherapy reduces this risk.