Answer:
Family members have a similar genetic make-up that may make them predisposed to cancer.
Step-by-step explanation:
Variation in certain genes can increase the risk of developing certain cancers. This is why certain cancers run in families. There are lots of examples where the risk factor is small, but in some cases, the risk factor is very large.
For example, mutations in BRCA1 are very highly linked to the risk of breast cancer. As a result, many women with mutations in this gene opt to get a mastectomy to reduce their chances of developing breast cancer.