Factors Multiple A growing tumor requires plenty of nutrients, and to make sure it gets them the tumor secretes substances that stimulate the growth of new blood vessels. See chart below Anti- metastatic Factors Multiple What kills most cancer patients is not the primary tumor but its metastatic spread. Scientists have identified a class of enzymes that enables cancer cells to enter the bloodstream by dissolving tissue and boring holes through capillary walls. New drugs could keep cancer cells confined to one spot. Many cancers, for example, have been found to contain mutations in the ras oncogene, and companies are racing to develop drugs that inhibit its growth-promoting activity.
Many breast cancers depend on the female hormone estrogen to stimulate their growth.
Tamoxifen, which acts as an antiestrogen in the breast, has been shown to prevent the development of this form of cancer. Preliminary evidence suggests that a newer compound, raloxifene, may confer a similar benefit without serious side effects. Compounds know as retinoids, derivatives of vitamin A, can prevent recurrence of certain head and neck cancers. In tumors, genes that are supposed to serve as checks on runaway cell growth are often so damaged that they stop functioning. Preliminary evidence suggests that this approach can sometimes cause tumors to stop growing and even shrink in size.