Some precancerous conditions progress through a series of growth alterations before becoming cancerous. For example, cervical cancer progresses from squamous metaplasia to squamous dysplasia to carcinoma in situ, and finally to invasive cancer. Endometrial cancer progresses from endometrial hyperplasia to atypical endometrial hyperplasia to carcinoma in situ, and finally to invasive cancer.
Cancer (Box 1) results from a series of genetic alterations that can include the following:
• Activation of oncogenes that promote cell growth
• Loss of tumor suppressor gene activity, which inhibits cell growth
Mutation or overexpression of oncogenes produces proteins that can stimulate uncontrolled cell growth, whereas mutation or deletion of tumor suppressor genes results in the production of nonfunctional proteins that can no longer control cell proliferation. The mutant cell multiplies and the succeeding generations of cells aggregate to form a malignant tumor.
Interleukin-24 (IL-24), initially called MOB-5, is a protein that is usually secreted by immune system cells in response to injury or infection. Research on colon cancer cells has demonstrated that IL-24, in conjunction with its receptors, appears to give a cancer cell the ability to fuel its own growth. The secreted proteins are released from one cell to transmit a signal to grow, migrate, or survive to another cell. These proteins cannot act alone and must act through a receptor or receptors on the receiving cell.
Box1. The Process of Cancer
