Clinical expression of the disease is seen when the inherited mutation of one apc allele is followed by a second hit mutation or deletion of the second allele.
Answers
What drives cancer cells to grow and divide uncontrollably and to escape cell death? Studies of mutations in tumor suppressor genes have provided key answers to this question. Tumor suppressor genes often function to restrain inappropriate cell growth and division, as well as to stimulate cell death to keep our cells in proper balance. In addition, some of these genes are involved in DNA repair processes, which help prevent the accumulation of mutations in cancer-related genes. In this way, tumor suppressor genes act as "brakes" to stop cells in their tracks before they can take the road to cancer. Given this situation, loss of tumor suppressor gene function can be disastrous, and it often puts once-normal cells on the fast track to disease.