Earlier detection and better treatments are helping drive down breast cancer death rates, American Cancer Society researchers report. Although the decline isn't huge -- 2.3% per year since 1990 -- it has been steady. What's more, women of all ages have seen breast cancer death rates drop, although the decline has been greatest in women under age 50.

The findings are part of Breast Cancer Facts & Figures 2005-2006, an ACS report on recent trends in the disease that is published every other year. Breast cancer is the most common cancer among US women (other than skin cancer), striking more than 200,000 each year and killing more than 40,000.

"The steady decrease in death rates since 1990 shows that we are making progress against breast cancer," said Stephen F. Sener, MD, national volunteer president of the ACS.

But there's more progress to be made, he noted.

The incidence of breast cancer is still increasing slightly in the US, although only among women 50 and older. Between 1987 and 2002, it went up by just 0.3% per year overall. Among women 40-49, however, incidence declined. Rates remained steady in women younger than 40.

And incidence still appears to differ according to race and ethnicity. Between 1992 and 2002, the report shows that breast cancer rates went up among Asian Americans and Pacific Islanders. But rates went down among American Indians and Alaska Natives, and did not change among whites, African Americans, or Hispanics/Latinas.

The report suggests changes in women's reproductive patterns are largely behind the rise in breast cancer rates. More women are waiting until later in life to have children, and are having fewer children overall. Becoming pregnant before age 30 and having multiple pregnancies can both lower the risk for breast cancer.

Learning more about the risk factors for breast cancer is an important goal of research into the disease, the report says. Scientists are examining lifestyle factors -- diet and exercise, for instance -- and genetic and environmental factors that might play a role in how breast cancer forms.

Investigators are also looking for drugs that could prevent breast cancer from forming in the first place. Tamoxifen is one drug already known to help reduce cases of breast cancer in high-risk women. Researchers are also studying raloxifene for this purpose, as well as aspirin and aspirin-like drugs.

Research into better treatments and earlier detection of breast cancer is also under way, the report says. Doctors are looking for ways to make mammograms more accurate, and for new technologies that may be even better than mammograms. Likewise, researchers are using new knowledge about the biology of breast cancer cells to develop new drugs that might work better against the cancer with fewer side effects.

Supporting such research is a priority for ACS, said Sener.

"This year the Society is supporting 175 research projects totaling $98.2 million, studying everything from biological pathways that turn benign breast lesions into cancer, to the relationship between tumor growth and body mass index," he said.