Breast Cancer - A Disease of a Susceptible Subgroup of Women

摘要

Background: The risk of bilateral breast cancer is substantially higher than the risk of unilateral disease and associated with early age at onset of the initial breast cancer. Of the many established risk factors for breast cancer, only family history has been consistently shown to be associated with bilateral disease. Methods: We analyzed a population-based cohort of 123, 757 women with a first primary breast cancer diagnosed in Sweden from 1970 to 2000 and identified 6,550 women with a bilateral breast cancer. Results: Incidence of synchronous bilateral breast cancer mimics that of unilateral breast cancer. During 20 years from initial diagnosis, the incidence of metachronous cancer decreased from about 800 to 400 per 10(exp 5) person-years in patients first diagnosed before age 45, whilst the incidence remained stable at 500 to 600 per 10(exp 5) among those who were older at diagnosis of first cancer. Conclusions: The finding of breast cancer being simultaneously diagnosed in two breasts has an incidence far beyond the expected, but is probably not explained by genetic background rather environmental factors. The incidence pattern of metachronous bilateral cancer by age and follow-up time fits neither a model of highly penetrant genes, nor a model assuming only aggregation of environmental risk factors.