Breast cancer diagnoses took sudden drop in '03

For the first time in decades, the number of women diagnosed with breast cancer fell dramatically in 2003 -- perhaps because millions of older women stopped taking hormone replacement pills at about that time, researchers said.

Overall, breast cancer rates in the United States declined 7 percent from 2002 to 2003, with the steepest decline -- 12 percent -- among women ages 50 to 69 diagnosed with a type of breast cancer that is fueled by the hormone estrogen, investigators said. About 14,000 fewer women were diagnosed with estrogen receptor-positive breast cancer in 2003 than in the previous year.

This is the first drop in breast cancer rates since at least 1975, said Donald Berry of M. D. Anderson Cancer Center in Houston, the study's senior investigator. Women are more likely to develop breast cancer as they age, so the study's figures are adjusted for the aging of the population.

Researchers, who discussed their findings at a meeting of breast oncologists in Texas yesterday, linked the drop to the bombshell news in July 2002 that hormone replacement therapy carried more risks than benefits, particularly increasing a woman's risk of developing breast cancer. Within months of the release of the study by the Women's Health Initiative, millions of women stopped taking estrogen and progestin to alleviate their symptoms of menopause.

"There are many possible explanations for this decline, but this is by far the most plausible," said Dr. Eric Winer, a breast cancer specialist at the Dana-Farber Cancer Institute who attended the meeting. "Especially given that the results were most dramatic in women over 50 who have hormone-positive breast cancer, it's very possible that relates to a dramatic reduction in women taking hormone replacement therapy."

The researchers who released their results yesterday were not able to definitively connect the decline in breast cancer rates to the decreased use of hormone therapy, but Dr. JoAnn Manson, principal investigator of the Boston branch of the Women's Health Initiative, said she and other investigators will use their large databases of women to see whether the hypothesis holds up. They will compare, for example, breast cancer rates of women who stopped taking hormone replacement therapy since 2002 with those who never took it.

Estrogen receptor-positive breast cancer is the most common and most treatable type of breast cancer. It accounts for about 75 percent of breast cancers and an even greater percent of breast cancer in women older than 50. It's unclear why rates of estrogen receptor-negative breast cancer also declined in 2003, although to a smaller degree.

Hormone replacement pills, around for decades, had been exploding in popularity during the 1980s and 1990s as a fountain of youth of sorts for aging women, and a way to help control hot flashes and other bothersome symptoms of menopause. By the early 2000s, about 30 percent of women over age 50 took the pills, authors of the study presented yesterday said. Now, most doctors prescribe hormone pills only to women who experience severe symptoms -- and for shorter durations, usually three to four years, or in low doses, several doctors said. Previously, many women remained on the pills indefinitely.

Dr. Ann Partridge, a breast oncologist at Dana-Farber who also attended yesterday's meeting, said what was striking about the study's results "was how quickly the decline seems to have occurred. Usually, when we make lifestyle changes that in theory might affect the risk of disease, it's like moving mountains.

"The other thing that is so exciting is the sheer magnitude of the decline," she added.

But the researchers and other oncologists said it is unclear whether the number of women diagnosed with breast cancer will continue to fall or whether women have merely delayed a cancer diagnosis by stopping hormone therapy.

It is likely that most women who were not diagnosed with breast cancer in 2003 had small tumors undetectable by a mammogram, Winer said. If they had continued taking hormone pills, which fuel tumor growth, their tumors might have been large enough to be detected by screening exams.

What's unclear is whether these tumors grew more slowly but have since been diagnosed or will be or whether by stopping hormone pills, their cancers will never develop to a point where they are detectable, treatable, or life-threatening.

"Whether [the decline] holds up over the course of many years, we'll have to see," Winer said. "For some of these women, it may result in a delay before diagnoses, which is not necessarily a bad thing. For some women, it may be that they're never diagnosed because their tumors shrank and became undetectable for the life of the woman. It's going to be very hard to sort this all out because of all the forces in play."

Berry said researchers will get an initial answer to this question in the spring, when breast cancer rates for 2004 become available, and they can determine whether the number of women diagnosed continued to decline and if so, at what pace.

Winer said it's important to keep in mind that estrogen receptor-positive breast cancer "is the least lethal type of breast cancer and responds very well to therapy. We still have an awful lot of work to do to prevent the cancers that are most lethal."