Breast cancer outcomes have improved over time, but more so in younger women than in those aged 75 years and older, according to findings from a review of data spanning nearly three decades.
The findings are concerning, because women aged 75 and older represent the fastest growing group of women affected by the disease, Dr. Benjamin D. Smith of the University of Texas M.D. Anderson Cancer Center, Houston, and his colleagues reported online in the Journal of Clinical Oncology.
According to data from National Vital Statistics Reports, breast cancer death rates began to decrease in 1990. Between that year and 2007, the breast cancer death rate in the general population declined by 2.5% per year among women aged 20-49 years, by 2.1% per year among those aged 50-64 years, and by 2.0% per year for those aged 65-74 years – but only by 1.1% per year for those aged 75 years and older.
Underlying factors that may account for the discrepancy include lower use of screening mammography in older women, lack of understanding regarding the optimal treatment for older women due to lack of representation of the older age group in clinical trials, conflicting evidence regarding the magnitude of benefit from adjuvant chemotherapy in different age groups, and a tendency to reduce chemotherapy dose intensity in older patients because of concern about increased risk of toxicity.
The "evolving disparity by age in breast cancer outcome" demonstrated by this study suggests research is needed "to understand preferences of older adults for screening and treatment and to identify optimal adjuvant therapy regimens that are both effective and tolerable in the setting of the functional status, comorbid illnesses, and social support of older women," the authors stated.
Based on data from 219,024 women diagnosed with breast cancer between 1980 and 1997 who were part of the Surveillance, Epidemiology, and End Results nine-registry cohort (SEER-9), the investigators reported that the risk of breast cancer death within 10 years decreased from 29.6% for those diagnosed in 1980-1984 to 20.1% for those diagnosed between 1995 and 1997, (J. Clin. Oncol. 2011 [doi:10.1200/JCO.2011.35.8408]).
"In multivariate analysis, the risk of breast cancer death decreased by a relative amount of 4.5% per diagnosis year after adjusting for age, race, and SEER registry," they said, adding that the 10-year absolute risk of breast cancer death from 1980 to 1997 decreased by 10.1% for women aged 20-49 years at diagnosis, by 15.3% for those aged 50-64 years at diagnosis, and by 12.5% for those aged 65-74 years at diagnosis – but only by 7.5% for those aged 75 years and older at diagnosis.
From 1980-1994, the older women experienced the lowest risk of 10-year breast cancer death at 24.8%, compared with rates ranging from 28.0% to 31.9% for the other age groups, but by 1995-1997 the older women experienced a higher risk of breast cancer death than other postmenopausal women (17.3% vs. 15.4%-16.6%), they said.
The findings demonstrate that both the rate of breast cancer death in the general population and the risk of breast cancer death in newly diagnosed patients decreased two to three times more rapidly for younger women, compared with women aged 75 and older, the investigators said, noting that it appears older women "may have missed out on advances in breast cancer diagnosis and treatment."
"Notably, approximately 40,000 women [aged 75 years or older] are diagnosed with breast cancer each year in the United States ... older women are the most rapidly growing cohort of patients with breast cancer, with 57% growth expected over the next 20 years as the US population ages," they wrote, adding: "Although our data provided reassurance that younger women have experienced substantial gains in breast cancer outcomes as a result of improvements in screening and treatment, these gains do not appear to have fully extended to the oldest 20% of patients with breast cancer."
Of note, the investigators also found race-based disparities in breast cancer outcomes. The findings indicate that, "black women are another sociodemographic group that has not fully reaped the benefits of improved breast cancer outcomes," they said, noting that the race-based gap emerged in the 1980s and continues to increase.
Dr. Smith reported receiving research funding from Varian Medical Systems. Another study author, Dr. Arti Huria, reported receiving research funding from Celgene, GlaxoSmithKline, and Abraxis BioScience, as well as serving as a consultant or in an advisory role for Genentech, Amgen, and GTx. The study was supported in part by a philanthropic gift from Ann Cazalot and Clarence Cazalot.