The purpose of the study was to identify overall incidence and risk of developing a metachronous contralateral testicular germ cell tumor (TGCT) and compare the risk for patients treated before and after 1980 (cisplatin became available for patients with metastatic TGCT). Our hypothesis was that the risk of metachronous TCGT would be reduced for patients with metastatic disease diagnosed after 1980. We included 7,102 men with unilateral TGCT, recorded in the Cancer Registry of Norway. Allowing for competing risk, cumulative incidence and adjusted hazard ratio (HR) were estimated for different subgroups, and the diagnostic periods 1953-1979 (I) and 1980-2007 (II). Relative risks were assessed by standardized incidence ratio (SIR). In Period I and Period II, 38 and 137 males, respectively, were diagnosed with metachronous contralateral TGCT. Corresponding 20-year cumulative incidences were 1.9% and 3.9%. In Period II, risk of a second TGCT was halved [HR = 0.5, 95% confidence interval (95% CI) = 0.33-0.77] for patients with metastatic compared to localized disease. For patients presenting with localized and metastatic disease, the SIRs for Period I were 14.6 (95% CI = 9.6-21.2) and 25.3 (95% CI = 12.1-46.5), respectively. In Period II, the corresponding numbers were 19.0 (95% CI = 15.6-22.9) and 9.8 (95% CI = 6.4-14.5). In conclusion, the risk of metachronous contralateral TGCT was halved for patients with metastatic compared to localized disease in Period II, whereas this protective effect of extent of disease lacked significance for Period I. These findings support our hypothesis that cisplatin-based chemotherapy reduced the risk of a second TGCT for patients with metastatic TGCT diagnosed after 1980.
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