Basal-cell carcinoma
Basal-cell cancer is a very common skin cancer. It is much more common in fair-skinned individuals with a family history of basal-cell cancer and increases in incidence closer to the equator or at higher altitude. There are approximately 800,000 new cases yearly in the United States alone. Up to 30% of Caucasians develop basal-cell carcinomas in their lifetime. In Canada, the most common skin cancer is basal-cell carcinoma (as much as one third of all cancer diagnoses), affecting 1 in 7 individuals over a lifetime.
Breast cancer
In the United States, 10 to 20 percent of people with breast cancer and people with ovarian cancer have a first- or second-degree relative with one of these diseases. The familial tendency to develop these cancers is called hereditary breast–ovarian cancer syndrome. The best known of these, the "BRCA" mutations, confer a lifetime risk of breast cancer of between 60 and 85 percent and a lifetime risk of ovarian cancer of between 15 and 40 percent. Some mutations associated with cancer, such as "p53", "BRCA1" and "BRCA2", occur in mechanisms to correct errors in DNA. These mutations are either inherited or acquired after birth. Presumably, they allow further mutations, which allow uncontrolled division, lack of attachment, and metastasis to distant organs. However, there is strong evidence of residual risk variation that goes well beyond hereditary "BRCA" gene mutations between carrier families. This is caused by unobserved risk factors. This implicates environmental and other causes as triggers for breast cancers. The inherited mutation in "BRCA1" or "BRCA2" genes can interfere with repair of DNA cross links and DNA double strand breaks (known functions of the encoded protein). These carcinogens cause DNA damage such as DNA cross links and double strand breaks that often require repairs by pathways containing BRCA1 and BRCA2. However, mutations in "BRCA" genes account for only 2 to 3 percent of all breast cancers. Levin "et al." say that cancer may not be inevitable for all carriers of "BRCA1" and "BRCA2" mutations. About half of hereditary breast–ovarian cancer syndromes involve unknown genes.