During follow-up, 141 women (31.3%) left the study (Table 4), either because women declined further participation (true drop-out) or follow-up ended if the follow-up period of 5 years was completed (5.5%), genetic testing did not show a BRCA1/2 mutation (0.7%), women underwent preventive mastectomy (2.7%), or breast cancer developed. The gene discussed is BRCA1; the disease is breast cancer.