TUESDAY, April 3, 2007 (HealthDay News) -- Recent declines in U.S. breast cancer death rates have been most significant among women with what are known as "estrogen receptor (ER)-positive" tumors and women younger than 70, a new study finds.
About 75 percent of breast cancer cases are ER-positive -- which means their tumors respond to circulating estrogen -- and the average age of breast cancer patients at the time of diagnosis is 62.
The study, published online April 2 in the Journal of Clinical Oncology, looked at national data on almost 235,000 cases of invasive female breast cancer.
They found that death rates declined by 24 percent between 1990 and 2003; from a peak of 33 deaths per 100,000 women per year to 25 per 100,000 per year.
Among women younger than 70, the death rate declined 38 percent for those with ER-positive tumors, compared with 19 percent for those with ER-negative tumors. Among women 70 and older, the death rate declined 14 percent for those with ER-positive tumors but did not decline for those with ER-negative tumors.
"These trends in breast cancer mortality since 1990 are likely attributable to at least two important factors: the use of tamoxifen after surgery, which substantially reduces the risk of recurrence in ER-positive tumors only; and widespread use of screening mammography, which is more likely to detect the slow-growing tumors that tend to be ER-positive," study lead author Dr. Ismail Jatoi, director of the Breast Cancer Center in the Department of Surgery at the National Naval Medical Center, said in a prepared statement.
The study did not investigate why there was less of a decline in breast cancer death rates among older women. However, the researchers noted that previous studies suggested that older women are less likely to receive adjuvant therapy for breast cancer.
The American Cancer Society has more about breast cancer.