Prostate cancer incidence and survival in immigrants to Sweden

Purpose: The large international variation in the incidence of prostate cancer (PC) is well known but the underlying reasons are not understood. We want to compare PC incidence and survival among immigrants to Sweden in order to explain the international differences. Methods: Cancer data were obtained from the Swedish Cancer Registry. Standardized incidence ratios (SIRs) were calculated for PC in first-degree immigrants by country of birth. The immigrants were classified into four groups by SIR and area of origin. Survival in PC was assessed by hazard ratio (HR) in the four groups. In some analyses, clinical stage of PC was assessed by the tumor, node, and metastasis classification. Results: The SIR was 0.47 (95 % confidence interval 0.43-0.51) for immigrants with the lowest risk, constituting men from Turkey, Middle East, Asia, and Chile. The HR was 0.60 (0.45-0.81) for these men and it was 0.49 if they had stayed 20+ years in Sweden. The SIR in screening detected PC, T1c, was 0.55. Among these men, screening detected PC constituted 34.5 % of all PC, compared to 29.0 % among Swedes (p = 0.10). Conclusions: The results showed that the non-European immigrants, of mainly Middle East, Asian, and Chilean origin, with the lowest risk of PC, also had the most favorable survival in PC. As the available clinical features of PC at diagnosis or the distribution of known risk factors could not explain the differences, a likely biological mechanism through a favorable androgenic hormonal host environment is suggested as an explanation of the observed effects.