Study finds advances in breast cancer don't extend to older women
The survival rates for older women with breast cancer lag behind younger women diagnosed with the disease, indicating that the elder population may be missing out on improvements in treatment and detection, according to new research from the University of Texas MD Anderson Cancer Center.
The study, published in the Journal of Clinical Oncology, is one of the first to identify whether the improvements made in breast cancer outcomes over the past three decades have been experienced by women of all ages, or only by certain age subsets.
Describing groups not experiencing proportionate improvements is critically important to identify sub-populations in need of targeted research, according to Benjamin Smith, M.D., assistant professor in MD Anderson's Department of Radiation Oncology.
"What surprised me was just how different the outcomes of older women are compared to those of other age groups," said Smith, the study's lead author. "In almost all other subsets, we found improvements that cluster in a similar direction, but older women are on a very different slope as far as the minimal improvement they've experienced."
Smith and his colleagues examined change over time for two outcomes: the rate of breast cancer death in the general population and the risk of breast cancer death in newly diagnosed patients and compared this change over time across age spectrums.
Data from the National Vital Statistics Report, published by the Centers for Disease Control and Prevention, from 1980-2007 categorized the rate of breast cancer death into four age groups: 20-49; 50-64; 65-74 and 75 and older. The Surveillance, Epidemiology, and End Results (SEER) registry, complied by the National Cancer Institute, was used to analyze the risk of breast cancer death from a cohort of 219,024 women ages 20 and older diagnosed from 1980-1997.
Results Show Discrepancy
Breast cancer death rates were stable throughout the 1980s for women ages 20-64, but increased for women ages 65 and older. Between 1990 and 2007, the largest decrease in death rates was seen in women ages 20-49 at 2.4 percent per year, a finding Smith attributes in part to the widespread dissemination of mammography, use of endocrine therapy and adjuvant chemotherapy. The smallest decrease in breast cancer death rates was seen in women ages 75 and older, at 1.1 percent per year.
The researchers also looked at the risk of breast cancer death. In 1980-1984, women ages 75 and older had the lowest risk of 10-year breast cancer death, 24 percent. In contrast, those younger than 75 had 10-year breast cancer risk that ranged from 29 percent to 31 percent. By 1995-1997, the risk for women ages 75 and older was 17.3 percent, compared to younger women who ranged from 15.4 percent to 16.6 percent.
Additionally, the study determined that black women with breast cancer are not seeing improvements in outcomes, evidenced by an absolute death rate in 2006 that was 38 percent higher than whites.
"We found that the oldest women, regardless of their race, and blacks, regardless of their age, are not benefiting as much from improvements in breast cancer treatments," Smith said.
Interestingly, explained Smith, less lethal estrogen receptor positive cancers are more common in older women, yet outcomes have still improved more rapidly for younger women who have a larger proportion of biologically aggressive disease. This suggests outcomes may be tied to suboptimal treatment rather than tumor biology.
While the study didn't examine root causes, Smith said several factors may account for the findings, including: the lowest mammography rates for older women; limited knowledge of optimal treatment resulting from under-representation or exclusion in clinical trials; and chemotherapy toxicity, which limits the ability to deliver therapy at recommended dosages.
According to the American Cancer Society, more than 230,000 women will be diagnosed with breast cancer in 2011. Of those women, about 40,000 are ages 75 and older, said Smith, making them the fastest growing segment of the breast cancer population. Future research is needed to understand this evolving disparity.
"Given the fact that breast cancer is growing rapidly, we really need to focus research exclusively on developing optimal treatments for older women with breast cancer, evaluating how we can predict which older women can tolerate treatments, and develop new treatments that work better," Smith said.