INSTEAD of killing off cancer cells with toxic drugs, scientists have discovered a molecular pathway that forces them to grow old and die. Cancer cells spread and grow because they can divide indefinitely. But a study in mice showed that blocking a cancer-causing gene called Skp2 forced cancer cells to go through an aging process known as senescence - the same process involved in ridding the body of cells damaged by sunlight. If you block Skp2 in cancer cells, this process is triggered, Pier Paolo Pandolfi of Harvard Medical School in Boston and colleagues reported in the journal Nature.