IT IS now clear that susceptibility to breast and ovarian cancer is inherited in some families. Between 5% and 10% of breast cancer1,2 and ovarian cancer3 can be attributed to inheritance of a gene conferring high risk, followed by genetic changes specific to the target epithelial cells of the breast or ovary. For decades, there has been no doubt that cancer is genetic, in the sense that transformation of a normal cell to invasive and malignant growth is due to changes in the DNA. But most cancer is genetic only at the level of the transformed cell, not in the germline cells of patients. Consequently, most cancer is not inherited in families. Not all that is genetic is inherited.
Meanwhile, it has been observed for centuries that breast cancer clusters in families.4 Of course, given the very high incidence of breast cancer in our times, there are
King M, Rowell S, Love SM. Inherited Breast and Ovarian Cancer: What Are the Risks? What Are the Choices? JAMA. 1993;269(15):1975–1980. doi:10.1001/jama.1993.03500150087033
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