Which types of cancer are hereditary?

Garber explains that between 5 and 10 percent of most kinds of cancers are found in a hereditary form, in which an identifiable genetic mutation is passed down through a family and confers a higher cancer risk. One example is mutations in the BRCA1 and BRCA2 genes, which increase the risk of developing breast cancer. Another 5 to 10 percent of cancers seem to be passed down in families but there is no single identifiable genetic mutation; in these cases, the increased susceptibility may stem from a cluster of genes. The rest of cancer cases have no observable hereditary component. They develop from genetic changes that take place in individual cells over a person’s lifetime.

This pattern of inheritance is seen in most types of cancer, and there is no one cancer type that is passed down in families more than others. Garber notes that a susceptibility to cancer is not necessarily inherited just because multiple members of a family get the disease. “Sometimes it’s just chance,’’ she says. One in two men and one in three women will develop some type of cancer in their lifetime, so the disease is common enough that it can appear multiple times in a family without a distinct genetic connection. And the occurrence of familial cancers is rare enough that if one of your parents develops a particular kind of cancer, the odds are that you will not.

When families do have an inherited susceptibility to cancer, the same kind of cancer appears in multiple generations of the family and tends to emerge earlier in life than normal. Garber notes that it’s also possible for a family to have an increased risk of cancer because of the shared environment in which they live, or because of behaviors like smoking that are passed on from generation to generation, rather than genetics.