Since 1990, the overall breast cancer death rates in the United States have decreased by about 24 percent, researchers report in the Journal of Clinical Oncology.

While the rates have declined for women with estrogen receptor (ER)-positive or ER-negative tumors, lead investigator Dr. Ismail Jatoi told Reuters Health, the decrease has been greater for women with ER-positive tumors and younger women.

The growth of estrogen-receptor positive breast cancers is stimulated by body’s own production of this hormone. Drugs such as tamoxifen work by blocking the effects of this estrogen on the breast tissue.

Jatoi of the National Naval Medical Center, Bethesda, Maryland and colleagues examined data contained in nine tumor registries that included almost 235,000 breast cancer cases diagnosed between 1990 and 2003.

During the study period, the risk of death in women younger than 70 years old with estrogen-receptor positive tumors fell by 38 percent, whereas the decline in women with estrogen-receptor negative tumors was just 19 percent.

In women older than 70 years, a 14-percent drop in death rates due to estrogen-receptor positive breast tumors was observed, but no there was no change in women with estrogen-receptor negative tumors.

“We speculate that these trends are at least partly due to mammography screening and the widespread use of tamoxifen in the 1990s,” Jatoi commented.

“Although mortality in all groups remains unacceptably high,” the investigators conclude, “additional emphasis should be placed on improving outcomes of breast cancer patients older than 70 years and those of all ages with estrogen-receptor negative tumors.”

SOURCE: Journal of Clinical Oncology, May 1, 2007.