Large tumors increased in ’90s

A new analysis shows a small but surprising upswing during the 1990s in the proportion of women with newly diagnosed breast cancer who have unusually large tumors, which are more likely to prove fatal.

Experts are uncertain why this happened, but they speculate that obesity and hormone replacement therapy may have fueled the growth of larger cancers, even during a time when the discovery of small tumors rose dramatically as a result of widespread mammography.

The analysis, prepared by the American Cancer Society, found that the incidence of large tumors increased by just over 2 percent a year between 1992 and 2000, but only in white women.

"The great majority of tumors in white women are small and at a localized stage," said Dr. Michael Thun, senior author of the report. "But we were surprised to see there has been an increase in tumors of five centimeters or more."

The hormone estrogen can fuel the growth of breast cancers. Thun said the most likely explanation for the rising tumor size is increases in women’s estrogen levels resulting from obesity and hormone replacement therapy, or HRT, after menopause.

Fat tissue itself makes estrogen. About two-thirds of U.S. women over 50 are overweight. The cancer society estimates weight contributes to between one-third and one-half of all breast cancer deaths among older women.

The use of hormone replacement pills, which includes estrogen, has fallen since last year, when a study showed that the widely used treatment after menopause increases the risk of breast cancer, heart attacks and stroke. That study found breast tumors were slightly larger, on average, among the hormone users.

"Is it biologically tenable that HRT and obesity could have contributed? The answer is clearly yes," said Dr. Larry Norton, deputy physician-in-chief for breast cancer programs at Memorial Sloan-Kettering Cancer Center in New York City.

The analysis is based on the National Cancer Institute’s Surveillance, Epidemiology and End Results program, a database of cancer incidence and survival data that covers about 14 percent of the U.S. population. It was published in the latest issue of the cancer society’s journal CA.

In 2000, there were 6.3 cases of breast cancer larger than five centimeters for every 100,000 white women in the United States, compared with 5.6 cases in 1992. Still, smaller tumors are much more common. In 2000, there were 90 tumors size two centimeters or smaller per 100,000 and 34 that were between two and five centimeters.