Taking the hormones for five years doubles the risk for breast cancer, according to a new analysis of the Women’s Health Initiative, a large federal study, revealing the most dramatic evidence yet of the dangers of the popular pills, the Associated Press writes.

Even women who took estrogen and progestin pills - Wyeth sells the combo as Prempro - for as little as a couple of years had a greater chance of getting cancer. And when they stopped taking them, their odds quickly improved, returning to a normal risk level roughly two years after quitting, the AP reports adding, that, collectively, these new findings are likely to end any doubt that the risks outweigh the benefits for most women.

The rate of breast cancer clearly plunged in recent years mainly because millions of women quit hormone therapy and fewer newly menopausal women started on the treatment, according to Rowan Chlebowski of Harbor-UCLA Medical Center in Los Angeles, the study leader. “It’s an excellent message for women: You can still diminish risk (by quitting), even if you’ve been on hormones for a long time,” said Claudine Isaacs of Georgetown University’s Lombardi Comprehensive Cancer Center. “It’s not like smoking where you have to wait 10 or 15 years for the risk to come down.”

The study results were released over the weekend at the San Antonio Breast Cancer Symposium, and were taken from the WHI, which tested estrogen and progestin pills that docs long believed would prevent heart disease and bone loss in women after menopause. The main part of the study was stopped in 2002 when researchers saw higher risks of heart problems and breast cancer in hormone users. Last week, by the way, the US Senate Finance Committee began a probe into charges Wyeth used ghostwriters for journal articles to boost declining Prempro sales (back story).

Since then, experts have debated whether the risks apply to women who start on hormones when they enter menopause, usually in their 50’s, and take them for shorter periods of time. Most of the women in the federal study were in their 60’s and well past menopause. So the advice has been to use hormones only if symptoms like hot flashes are severe, and at the lowest dose and shortest time possible. The new study sharpens that message, Chlebowski tells the AP.

Even so, most women will not get breast cancer by taking the pills short-term. The increased cancer risk from a couple of years of hormone use translates to a few extra cases of breast cancer a year for every 1,000 women on hormones. This risk accumulates with each year of use, though.

The WHI study had two parts. In one, 16,608 women closely matched for age, weight and other health factors were randomly assigned to take either Wyeth’s Prempro - estrogen and progestin - or dummy pills. This part was halted when researchers saw a 26 percent higher risk of breast cancer in those on Prempro.

But that was an average over the 5 1/2 years women were on the pills. For the new study, researchers tracked 15,387 of these women through July 2005 and plotted breast-cancer cases as they occurred over time. They saw a clear trend: Risk rose with the start of use, peaked when the study ended and fell as nearly all hormone users stopped taking their pills.

In the second part of the federal study, researchers observed just 16,121 women who had already been on hormones for an average of seven years and another group of 25,328 women who had never used them. No results on breast-cancer risk in these women have been given until now.

Plotting cases over time, researchers saw in retrospect that hormone users had started out with twice the risk of breast cancer as the others, and it fell as use declined. Among those taking hormones at the start of the study, use dropped to 41 percent in 2003, the year after the main results made news.

Source: The Associated Press