POTENTIAL SOLUTIONS TO THE PROBLEM of cancer seem limited only by the imagination. In some promising new therapies, the body's internal weapons are trained on cancerous growths. In other treatments, no less a powerful element than light is employed to eradicate the invaders. Still other research focuses on stopping the tumor's blood supply.

						Blocking the Pathways of Cancer Prodded by growth-promoting oncogenes, freed from the restraints of suppressor genes, cancer cells move through a series of steps in their quest to establish tumors. Through the mechanisms of metastasis, invasion and angiogenesis, the renegade cells undertake an "arduous marathon." In 1992 researchers began testing methods to foil metastases, using drugs to block necessary enzymes in the cancer cells and others that arrest the growth of new tumors. To metastasize, or spread, cancer cells detach themselves from the tumor and leak into nearby blood vessels. These roving cells move through the circulatory system until they find a suitable place to breach the vessel wall again and invade the surrounding tissues. The human body produces its own defense, the non-metastatic 23 (nm23) tumor suppressor gene, the presence of which has proved a powerful predictor of survival among breast cancer patients.

		Immunotherapy: The Body's Own Weapons Researchers have also harnessed the body's own complex immune system to defend against cancer. By linking monoclonal antibodies to lethal toxins derived from plants or bacteria, researchers such as Ellen Vitetta and Ira Pastan realized the dream of a "magic bullet": the tailor-made antibody delivers its deadly cargo directly to its target cell.

		Harnessing the Immune System In 1993 Gary Nabel treated patients with melanoma by injecting genes encased in fat droplets into tumors.The gene he used coded for a protein which arouses the immune system. When the cancer cells incorporated the gene and began producing the telltale protein, immune cells attacked. These experiments demonstrated the possible uses of direct gene transfer in human cancer treatment.

		Taking Aim With Light Photodynamic therapy employs a photosensitizing agent injected into the body to make cells ultrasensitive to light. The agent quickly passes through normal cells, but lingers in cancerous ones. The treated cancer cells are then exposed to light from a laser, which destroys them while doing little damage to the normal cells in the area.
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