updated 7/29/2005 6:33:12 PM ET 2005-07-29T22:33:12

The U.N.’s cancer research agency added hormone pills Friday to the list of substances that can cause cancer.

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The International Agency for Research on Cancer said that based on consistent evidence from studies in recent years, it was reclassifying hormonal menopause therapy from “possibly carcinogenic” to “carcinogenic.”

The declaration from the World Health Organization’s cancer agency, which is widely regarded as the international authority on cancer-causing agents, comes after several recent high-profile studies linking combination hormone replacement therapy, or HRT, to breast cancer.

The analysis, conducted by a panel of 21 scientists, concluded that estrogen and progestin therapy for menopause also slightly increases the risk of endometrial cancer when progestin is taken fewer than 10 days a month.

Research has indicated that the chance of a woman developing breast cancer during her lifetime is about 1 in 7. A landmark study used in the U.N. agency’s analysis suggested that long-term use of hormones raises the lifetime risk to about 1 in 6.

The cancer research agency also concluded that a common type of birth control pill, taken by about 10 percent of women of reproductive age, increases the risk of more types of cancer than previously thought.

Some doctors cautioned that that conclusion was based on studies of higher-dosage pills, and said they wouldn’t change their advice to young women.

'A complicated picture'
The agency had previously determined that the pill combining estrogen and progestin can cause liver cancer. Now, further research has demonstrated that it also slightly increases the risk of breast and cervical cancer, the agency said. However, the investigation also confirmed that the pill protects against endometrial and ovarian cancers.

“It’s a complicated picture,” said Vincent Cogliano, head of the agency’s department that evaluates the cancer risk of chemicals. “There are still other reasons to take it. Each woman has to discuss it with her doctor and weigh the risks and benefits” for either the contraceptive pill or hormone replacement therapy.

The increased cancer risk from the birth control pill was small and transient, the analysis found.

While experts did not dispute the agency’s conclusions on hormones for menopause, some were less convinced about the dangers of the birth control pill.

“I think it’s flat-out wrong,” said Dr. Steven R. Goldstein, professor of obstetrics and gynecology at New York University Medical Center. “Most of the studies were using pills 2½ to four times the dosage that I’m using today in most women.”

“My advice to women is absolutely no different tomorrow than it was yesterday,” Goldstein said. “In nonsmokers who have normal blood pressure, I think the benefits outweigh the risk. I think there’s good science that they have less ovarian and uterine cancer and I don’t think there’s good science that they will have more breast cancer, especially in the doses and the way we are using it.”

Eugenia Calle, director of analytic epidemiology at the American Cancer Society, was also less convinced on the cancer dangers from the pill. Both she and Goldstein said they believed it was premature to tie it to cervical cancer.

“For the breast, there is evidence for a very small increase in risk, but it’s transient and goes away as soon as the pill is stopped. And these are used at a time of life when breast cancer rates are very, very low anyway,” Calle said, adding that it’s unclear whether the studies are revealing a cause of cancer or a promotion of cancer by providing an environment that encourages tumor cells to grow.

There are many drugs that can cause cancer, including cancer-fighting chemotherapies, immune-suppressing medications and radiation therapy.

© 2013 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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