TUESDAY, Feb. 7 (HealthDay News) -- The risk of dying from a hormone receptor-positive breast cancer increases with age, according to new research. And one reason might be that older women with breast cancer are undertreated compared to their younger peers.

For women between the ages of 65 and 74, the risk of dying from breast cancer was 25 percent higher than for women under 65. For those 75 and older, the risk of death was 63 percent higher than for women under 65, according to the new study.

"This study showed that among postmenopausal, non-metastatic, breast cancer patients, elderly patients have a higher risk of dying from breast cancer than younger patients," said study author Dr. Cornelis van de Velde, a professor of surgery at Leiden University Medical Center in the Netherlands and president of the European Cancer Organization.

Results of the study are published in the Feb. 8 issue of the Journal of the American Medical Association.

Breast cancer affects about 226,000 American women every year, according to the American Cancer Society. Worldwide, there were nearly 1.4 million new cases in 2008, according to background information in the study.

Breast cancer tumors can be either hormone receptor-negative or positive. If a tumor is hormone receptor-positive, that means that the tumor's growth is fueled by hormones, such as estrogen, progesterone or both. Certain treatments specifically target hormone receptor-positive cancers.

In the current study, researchers reviewed data from a previous trial of treatments designed for hormone receptor-positive breast cancers. The nearly 10,000 women included were randomly assigned to receive one of two drugs, exemestane (Aromasin) or tamoxifen (Nolvadex), for 2.5 to 3 years, and then all received Aromasin for an additional 2 to 2.5 years. The women were from nine different countries, and all had hormone receptor-positive breast cancer.

There were more than 5,300 women under age 65 in the study; over 3,000 women between the ages of 65 and 74; and just over 1,350 women above the age of 75.

Not unexpectedly, the overall risk of death from any cause was higher for older women. As women aged, the proportion of all-cause deaths attributed to breast cancer became smaller.

However, when the researchers looked at breast cancer-specific deaths, they found that older women were significantly more likely to die from breast cancer than younger women. The investigators also found that for every 10-year increase in age, the risk of death from breast cancer went up by 20 percent.

Van de Velde said the current study can't answer the reason why older women have a higher risk of death from breast cancer, but that "the most plausible explanation is that elderly patients may experience undertreatment."

Len Lichtenfeld, deputy chief medical officer at the American Cancer Society, commented on the findings.

"There has been an assumption that older women may have a more indolent course of breast cancer, and that there was more of a risk of overtreating older women," Lichtenfeld said. "This study suggests that the course of the disease isn't so indolent, and that breast cancer still plays a significant and increasing role in the risk of death in older women."

Lichtenfeld said that while the reasons aren't clear from this study, undertreatment is a possibility. He said there may be a concern about how well older women might handle the side effects of cancer treatments. It's also possible that there's something different in the breast cancer itself that may make it more aggressive, or breast cancers in older women may not respond as well to the available treatments.

Lichtenfeld also noted that other medications older women take could potentially interact with cancer treatments.

The study found that older women tended to have larger tumors at the time of diagnosis, which also could have affected their outcome. But, it wasn't clear if older women had larger tumors when diagnosed because of a lack of screening, or again, if it had something to do with the type of breast cancer they had.

"These data underline the need for age-specific breast cancer studies in order to improve breast cancer outcomes in all ages," van de Velde said.

Funding for the current study was provided by the Dutch Cancer Society. The initial trial received an education grant from Pfizer, the company that manufactures Aromasin.

More information

Learn more about available breast cancer treatments from the American Cancer Society.