What Is Hereditary Breast Cancer

It is worth stating at the outset that the term "hereditary breast cancer," while in widespread usage, is somewhat problematic. Hereditary implies that the propensity to disease in that individual has been inherited. Thus, the implication is that breast cancer can be dichotomized into those cases where susceptibility is inherited and those where it is not. This concept arose from consideration of cancers with a simpler genetic basis such as retinoblastoma and Wilm's tumor, which can be usefully categorized in this way (2,3). As we shall see, the situation is much more complex for breast cancer. There are many different susceptibility genes for breast cancer, and a substantial fraction (in fact the majority) of breast cancer cases occur in women who are predisposed in some way. It is also worth emphasizing here that there is no known pathologically distinct type of breast cancer that is hereditary (although certain pathological features are more common in BRCA1 carriers), so it is not sensible to think of "hereditary" breast cancer as a distinct disease entity.

In clinical genetics, "hereditary" cancer is often used in a more practical sense to denote cases with a strong family history of the disease, consistent with the inheritance of a single dominant gene. This is often distinguished from "sporadic" cancer, meaning no family history and "familial" cancer, meaning any family history of the disease. Familial by itself is a rather loose concept in that it depends on how detailed a family history has been taken. Since breast cancer is a common disease, some family history of breast cancer will be found in most women if the pedigree is extended far enough. However, if restricted to first-degree relatives, approximately 10% of breast cancer cases would be considered "familial." The proportion of women with a strong family history (say two affected first-degree relatives) is much smaller, but again it depends on how comprehensive a family history is available.

Distinguishing women with a strong family history is useful in practice, since such individuals are at higher risk of the disease and may be managed differently. However, it is important to emphasize though that "hereditary" is a misleading term for this group. Even a strong family history does not necessarily imply the presence of a high-risk disease-causing mutation (although it makes it more likely). Conversely, carriers of high-risk mutations may have no apparent family history, for example, if the mutation was inherited through their father.

A more rational approach to the management of women at increased risk of breast cancer is to categorize them according to their level of risk. Such information is the basis for management guidelines in several countries. This risk will depend on their family history and other risk factors and, increasingly, their genotype at known predisposition genes.

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