Among four unrelated cohorts from Holland, the United States, Tasmania, and France, which respectively included 190, 68, 71, and 536 women affected by MEN1 with a follow-up from 5 to 27 years, breast cancer has 2.3- to 2.8-fold penetrance than the control population, obtained from the respective national cancer registries (81). This evidence concerns the gene MEN1 and breast cancer.