No. Most cancer happens by chance, but some are caused by hereditary changes in genes. For example, about 5-10% of breast cancers and about 20-25% of ovarian cancers are due to inherited genetic changes that increase the risk to develop these types of cancer. A person may have an inherited change in a cancer gene even if cancer hasn’t occurred in their family. It is important to consult with a genetic counselor if you think that you or a family member might have a hereditary cancer risk.