Heredity and human cancer.

The dominantly inherited tumors of man demonstrate that mutation can be a step on the carcinogenetic pathway. Nonhereditary tumors may involve the same mutation in somatic cells rather than germ cells. In neither case is this mutation alone sufficient to produce a tumor, and evidence is presented that a second mutational step is required in the initiation process. Individuals who bear these mutations germinally are extremely susceptible to specific tumors, they may develop more than one tumor, and the average age at onset is earlier than usual. Recessive genes for cancer susceptibility and environmental carcinogens may interact with each other and with these dominant "cancer genes" to increase the probability that cancer mutations will occur.