Interest in hereditary influences emerged with the understanding that genetic alterations underlie the process of transformation of a normal cell into a cancer cell. The basis of cancer is the loss of normal genetic control of cellular processes. At the molecular level, cancer is a disorder of genes, particularly oncogenes and tumor suppressor genes. Among the estimated 50,000 genes in the human genome, only a small fraction seem to be essential for cancer development. Genetic alterations can lead to dysregulation of cell replication, DNA repair, apoptosis, and immune surveillance against tumor cells.
Inherited traits can interact with environmental carcinogens.
For example, sunlight increases skin cancers among genetically susceptible Celts and other light-skinned populations. Patients with albinism or xeroderma pigmentosum have a defect in excision repair of UV-damaged DNA and develop multiple skin cancers in exposed areas. Epidemiologic studies can help define the influences of both environmental carcinogens and host factors in cancer development. Hereditary factors in cancer development have been identified in studies of cancer families. Virtually every form of cancer manifests a tendency to aggregate in families.