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Why hormone therapy may increase the risk of several types of cancer

October 20, 2010
  • Image of a breast cancer cell.
Image of a breast cancer cell. (National Cancer Institute )

A study released Tuesday confirmed that estrogen-plus-progestin hormone replacement therapy increases the risk of breast cancer. The study, based on 11 years of following women in the Women's Health Initiative study, which analyzed the impact of hormone therapy on women's health, also found a slightly higher death rate from breast cancer among women who took hormones. But a different study published in the American Journal of Surgery in 2009 drew a different conclusion.

Dr. Stephen F. Sener, now chief of the division of surgical oncology at the Keck School of Medicine at USC, analyzed data from 1,055 patients over age 50 who had breast cancer. He found that hormone therapy users developed breast cancer at a younger age than nonusers but that the cancers were not as dangerous and that overall survival rates were higher in hormone users compared with women who developed the disease but had never taken hormones.

In an e-mail, Sener said he believes neither his study nor the study published Tuesday has enough patients to say definitively that hormone therapy increases the severity of breast cancer and deaths from the disease. "I think the jury is still out on survival after hormone replacement therapy," Sener said.

Why might hormones increase cancer risk? In 2009, a different study linked hormone use to a higher risk of lung cancer. Other studies have suggested hormones slightly increase the risk of ovarian and endometrial cancer, but may lower the risk of colorectal cancer.

In an interview Tuesday, the lead author of the new study, published in the Journal of the American Medical Assn., said hormones, especially progestin, stimulate the blood supply that feeds small tumors and causes them to grow -- a process called angiogenesis.

"With the lung cancer risk being increased and the breast cancer risk being increased, our hypothesis is that estrogen and progestin are potent angiogenesis stimulators," said Dr. Rowan T. Chlebowski, a medical oncologist at the Los Angeles Biomedical Research Institute. But, he added: "The cancer issue has really not been fully engaged by the medical community."

Here's a good resource on hormone therapy and cancer risk from the American Cancer Society.

Chlebowski's research group reported in a 2009 study in the New England Journal of Medicine that breast cancer rates have declined since the conclusions of the Women's Health Initiative and a majority of women stopped taking hormones. The new study, he said, confirms that disuse of hormone therapy is likely the reason for the falling breast cancer rate and that deaths from breast cancer are likely to decline, too.

A decade ago, hormone replacement therapy was considered important for women's ongoing health and vitality after menopause. The massive and expensive Women's Health Initiative, a randomized, controlled trial, has turned that concept on its head. However, many questions still remain about the role and risks of hormones, such as whether different (and lower dose) formulations of hormones increase the risk of disease and whether younger menopausal women on hormones also have increased risks. Until those questions are answered, it's likely that more women and their doctors will decide that the benefits aren't worth the risks.

Now, will someone please find a safe -- and really effective -- remedy for hot flashes and night sweats?

-- Shari Roan / Los Angeles Times

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