Knowledge of cancer genetics is advancing our biological understanding of breast, colon, prostate and lung cancers. A family history of any one of these four types of cancer can increase an individual's personal risk to also develop a malignancy. For some families, genetic testing, in combination with genetic counseling, can be a helpful way to identify a hereditary cancer predisposition gene or establish a cancer risk management plan. In this paper, we will review the current state of knowledge surrounding genetic factors influencing breast, colon, prostate and lung cancer.