LOS ANGELES, April 22 (Xinhua) -- U.S. scientists have discovered one of the reasons why bladder cancer is so much more prevalent in men than women, according to a new study.

    Researchers at the University of Rochester Medical Center pointed to a molecular receptor or protein that is much more active in men than women.

    This protein plays a role in the development of the disease. The finding could open the door to new types of treatment with the disease, the researchers said in an article in the April 4 issue of the Journal of the National Cancer Institute.

    The study showed that the androgen receptor, which is central to the action of testosterone and other hormones that are much more plentiful in men than women, appears to play a key role in the disease.

    In experiments reported in the journal, mice without the receptor had dramatically lower rates of bladder cancer compared to normal mice with the receptor, and human cancer cells with the receptor were much more aggressive than those without it. Mice develop bladder cancer for many of the same reasons people do, and the molecular signals that control cancer development in mice mirror those in humans.

    The disease hits about three times as many men as women, including estimates of 50,000 men and 17,000 women in the United States in 2007, according to the American Cancer Society.

    Some scientists have suspected that male hormones working in concert with the androgen receptor might play a role, but hard evidence has been minimal until now, said Edward Messing, M.D., a bladder cancer expert and chair of Urology at the university.

    Instead, scientists have suspected that factors like greater exposure of men to cigarettes and industrial chemicals has been responsible.

    "For many years, people have recognized that men are more likely than women to get bladder cancer," said Messing, one of the authors of the paper. "More and more women are smoking and working with chemicals in the workplace, yet their bladder cancer rates have not really changed much. There is no longer any question that the androgen receptor is playing a role in bladder cancer."