Age- and time-dependent changes in cancer incidence among immigrants to Sweden: colorectal, lung, breast and prostate cancers

To examine the role of gender, age at immigration and length of stay on incidence trends of common cancers, we studied risk of colorectal, lung, breast and prostate cancers in immigrants to Sweden from 1958 to 2008. The nationwide Swedish Family-Cancer Database was used to calculate standardized incidence ratios for common cancers among immigrants compared to Swedes. Immigrants were classified into high-risk countries when their risk was increased, into low-risk when their risk was decreased and into other when their risk was nonsignificant. Among those who immigrated at younger age (<30 years), we found an increasing trend for colorectal cancer risk in low-risk men and high-risk women. Among those who immigrated at older age (=30 years), a decreasing lung cancer risk in high-risk men and an increasing breast cancer risk in low-risk women were observed. The increasing trend of prostate cancer risk was independent of age at immigration. The risk trends for other immigrants were between the risks of low- and high-risk countries. The gender-specific shifts in cancer risks in immigrants toward the risk in natives indicate a major role of sex, age at immigration and environmental exposures in colorectal and lung cancers risks. In contrast, the unchanged trend of breast cancer among those who immigrated at younger ages and an increasing trend for those who migrated at older ages may suggest a limited effect for environmental exposures, especially at younger age. Our study points out a role of age at immigration on the risk trend of cancer.