The International Agency for Research on Cancer has reclassified hormonal menopause therapy from 'possibly carcinogenic to humans' to 'carcinogenic to humans.'

In a review of existing research, the International Agency for Research on Cancer declared Friday that based on consistent evidence emerging from studies published over the last few years, it has reclassified hormonal menopause therapy from "possibly carcinogenic to humans" to "carcinogenic to humans."

The declaration from the World Health Organization's cancer agency, which is widely regarded as the international authority on which substances cause cancer, 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-progestogen menopause therapy also increases the risk of endometrial cancer when progestogens are taken fewer than 10 days a month.

'Complicated Picture'

The group also concluded that the combination contraceptive pill, taken by about 10 percent of women of reproductive age, increases the risk of more types of cancer than previously thought.

The agency had previously determined that the pill 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.

Caution in Interpreting Conclusions Urged

While experts did not dispute the agency's conclusions on hormone replacement therapy, some were less convinced that current evidence proves the contraceptive pill is carcinogenic and urged caution in interpreting the conclusions.

"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 2 1/2 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 by the labeling of birth control pills as carcinogenic.

Both she and Goldstein said they believed it was premature to tie the birth control pill 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.