Genes And Breast Cancer Risk

Is there evidence for cancer proneness? It has been known for many years that a maternal history of breast cancer is a major breast cancer risk factor. This suggests that although many factors interact to increase or decrease breast cancer risk, genes and the family history are important in determining breast cancer proneness.

One study followed 20,341 women for six years, to determine whether they showed any evidence of unusual proneness to breast cancer. Results showed that women were about twice as likely to develop breast cancer if their mothers had the disease (Cancer, v.64 ; 1989 ; 582-590). If two or more close relatives were afflicted with breast cancer, a woman is four to six times more likely to develop the disease. Cancer risk is heightened if several close relatives developed breast cancer at an early age, or if the cancer affected both breasts. Based on the findings of the study, the hereditary component of risk is likely to induce breast cancer at a relatively young age. Excess risk declines with increasing age of the relative at diagnosis.

Thus, for the most common case of a woman whose mother had unilateral breast cancer diagnosed after the age of 60, the risk of breast cancer is only about 40% higher than that for the rest of the population.