Final answer:
Fewer than 10 percent of human cancers are believed to be associated with inherited mutations. BRCA1 and BRCA2 gene mutations greatly increase the risk for specific cancers like breast and ovarian cancer. Genetic testing can identify these mutations and help in assessing cancer risk.
Step-by-step explanation:
It is thought that inherited mutations are responsible for fewer than 10 percent of human cancers. Mutations in specific genes, such as BRCA1 and BRCA2, significantly increase the risk for certain cancers, notably breast and ovarian cancer. While the risk is notably higher in individuals carrying these mutations, not everyone who inherits them will develop cancer. For example, women with a harmful BRCA1 gene mutation face a 55 to 65% risk of developing breast cancer before the age of 70, compared to the 12% risk among the general female population.
Rebecca may question the genetic aspect due to a lack of cancer history in her family, but this does not negate the hereditary risk. Genetic testing can be done to determine inherited cancer-causing mutations, and her family's health history could indeed indicate an inherited component, especially if multiple family members were diagnosed with cancer at an early age or with certain cancer types.