The subsequent loss of a suppressor gene on chromosome 18 further stimulates the adenoma, and finally the loss of a gene on chromosome 17 converts the benign adenoma to cancer. Additional changes may make the cancer metastasize. Even when a cell becomes cancerous, the immune system can often destroy it before it replicates and becomes established as a cancer. Cancer is more likely to develop when the immune system isn't functioning normally, as in people with AIDS, those receiving immunosuppressive drugs, and those with certain autoimmune diseases. A host of genetic and environmental factors increases the risk of developing cancer.
Family history is one important factor.
Some families have a significantly higher risk of developing certain cancers than other families. For example, a woman's risk of developing breast cancer increases 1.5 to 3 times if her mother or sister had breast cancer. Some breast cancers are linked to a specific gene mutation, more common in some ethnic groups and families. Women with this gene mutation have an 80 to 90 percent chance of developing breast cancer and a 40 to 50 percent chance of developing ovarian cancer. Researchers have found that 1 percent of Ashkenazi Jewish women have this gene mutation.