Gene Implicated in Prostate Cancer

A gene linked to breast cancer may spur the growth of advanced prostate cancer, which kills some 44,000 American men each year. The finding, from a study of tumors transplanted into mice and reported this month in Nature Medicine, raises the prospect of one day treating prostate cancer with a drug that shrinks breast tumors in women.

Caught early, prostate cancer can be treated by chemically castrating the patient. At this stage, tumors crave androgens--male hormones such as testosterone--and will shrink if these are blocked by drugs. But eventually (typically after a few years) tumors learn to live without the hormones and begin to grow and spread again. Once this happens, no treatment can rein them in. The cancer weans itself from androgens, oncologist Charles Sawyers and his co-workers at the University of California, Los Angeles, believe, by developing a taste for the protein made by the gene HER-2/neu. The gene also enables some breast cancers to grow without estrogen.

Sawyers and company found that advanced stage prostate tumors grafted into mice contained many times more HER-2/neu protein than tumors in the earlier androgen-dependent stage. They also found that androgen-dependent tumors would grow without the hormones if they were infected with a genetically engineered virus loaded with the gene. The researcher concluded that the HER-2/neu protein stimulated androgen receptors in late phase cells, thus triggering continuous cell division without the need for androgens.

If HER-2/neu fuels the growth of advanced prostate cancer in humans, then the disease might respond to Herceptin, a breast cancer drug that ties up the HER-2/neu protein. But Tapio Visakorpi, an oncologist from the University of Tampere, Finland, whose commentary on the results also appears in Nature Medicine, warns, "There is still a very, very long way to go to say whether Herceptin will be helpful in treating prostate cancer." Visakorpi says that researchers should next determine whether HER-2/neu is as prevalent in advanced prostate tumors in men as it is in cancers grafted into mice. Sawyers, who intends to test Herceptin in mice, agrees. "My hope," Sawyers says, "is that this paper is going to force people to address this question."