Declines in HRT use associated with decreased breast cancer incidence

Researchers identified an absolute decline of about 14,000 fewer women diagnosed with breast cancer in 2003 than in 2002.

Issue: January 1, 2007

29th Annual SABCS SAN ANTONIO — Breast cancer incidence in the United States has dropped sharply and this decline might be due to the fact that millions of older women have stopped using hormone replacement therapy, according to research presented here at the 29th Annual San Antonio Breast Cancer Symposium.

The researchers reported that there was an overall 7% relative decline in breast cancer incidence between 2002 and 2003 and that the steepest decline (12%) occurred in women aged between 50 and 69 diagnosed with estrogen receptor–positive breast cancer. ER-positive breast cancer depends on hormones for tumor growth, according to the report.

From their data, the researchers concluded that as many as 14,000 fewer women were diagnosed with breast cancer in 2003 than in 2002, a year in which the American Cancer Society estimated 203,500 new cases of breast cancer were diagnosed.

“It is the largest single drop in breast cancer incidence within a single year I am aware of,” said Peter Ravdin, MD, PhD, a research professor in the department of biostatistics at the University of Texas MD Anderson Cancer Center in a press release.

“Something went right in 2003, and it seems that it was the decrease in the use of hormone therapy, but from the data we used we can only indirectly infer that is the case,” he said. “But if it is true, the tumor growth effect of stopping use of HRT is very dramatic during a short period of time, making the difference between whether a tumor is detected on a mammogram or not in 2003,” Ravdin said.

Hormonal therapy

Donald Berry, PhD, professor and head of the division of quantitative sciences at MD Anderson Cancer Center, said he was, at first, surprised by both the magnitude and the rapidity of the decline in incidence. However, he said that it makes sense if you consider that use of HRT may be an important contributing factor to breast cancer development.

“The incidence of breast cancer had been increasing in the 20 or so years prior to July 2002, and this increase was over and above the known role of screening mammography,” Berry said. “HRT had been proposed as a possible factor, although the magnitude of any HRT effect was not known. Now the possibility that the effect is much greater than originally thought all along is plausible, and that is a remarkable finding.”

HRT provides both estrogen and sometimes also progestin hormones to postmenopausal women. The ongoing Women’s Health Initiative study of 16,608 women aged 50 to 79 years using HRT was prematurely stopped in July 2002 when the combination of estrogen and progestin was found to significantly increase the risk for developing invasive breast cancer.

Ravdin said about 30% of women older than 50 had been taking HRT in the early years of this decade, and about half of these women stopped using HRT in late 2002 after the results of the large study were announced.

“Research has shown that ER-positive tumors will stop growing if they are deprived of the hormones, so it is possible that a significant decrease in breast cancer can be seen if so many women stopped using HRT,” he said.

Absolute decline

The researchers said that because the analysis was based solely on population statistics, they could not know for certain the reasons why incidence declined. “We have to sound a cautionary note because epidemiology can never prove causation,” Ravdin said. They considered whether other effects might be involved, such as decreased use of screening mammography and changes in the use of antiinflammatory agents or statins, but only the potential effect of HRT was strong enough to explain the effect.

To conduct the study, Ravdin, Berry and researchers at the NCI and Harbor UCLA Medical Center analyzed data from nine regions across the country that contribute data to the NCI’s Surveillance Epidemiology and End Results (SEER) database.

They examined rates of breast cancer in the United States from 1990 to the end of 2003 and found that although incidence increased at 1.7% per year from 1990 to 1998, it began to decrease, relative to other years, 1% each year from 1998 to 2002. When that 1% increase was adjusted for age in each of those years, incidence from 1998 to 2002 stayed about the same, Ravdin said. “There were more cases of breast cancer being diagnosed, but that was because women were getting older and entering the higher risk pool.”

By the end of 2003, there was a 7% age-adjusted decrease in the number of breast cancer cases diagnosed. With further analysis, the researchers discovered that decline in incidence was far greater in ER-positive breast cancer (8%) compared with ER-negative breast cancer (4%). When they looked at women aged 50 to 69 years old, the decline in ER-positive cancer was 12%, compared with 4% in ER-negative breast cancers. After adjusting for age, the researchers concluded that there was an absolute decline of about 14,000 fewer women diagnosed with breast cancer in 2003 than in 2002.

For more information:
Ravdin PM, Cronin KA, Howlander N, et al. A sharp decrease in breast cancer incidence in the Unites States in 2003. Abstract 5. Presented at: 29th Annual San Antonio Breast Cancer Symposium; Dec. 14-17, 2006; San Antonio.