Using the Swedish Family-Cancer Database, the increased risk of breast cancer in women with relatives with the disease did not vary with paternal/maternal lineage. Familial breast cancer heritable component was 73% and the environmental proportion 27%. Familial aggregation of breast cancer in women below age 51 years is mainly due to heritable causes.
Department of Neurobiology, Care Sciences and Society, Karolinska Institute, CeFAM, Alfred Nobels Allé 12, Plan 5, 141 83 Huddinge, Sweden. Elisabeth.Couto@ki.se
