WASHINGTON – For women aged 75 years and older, a span of 5 or more years between mammograms translated into a threefold increased risk of death from breast cancer, compared with women in the same age group who had yearly exams.
While the exact reasons for the finding can’t be pinpointed, it should at least reawaken the discussion about whether older women should get a regular mammogram, Dr. Michael Simon noted at the annual meeting of the American Association for Cancer Research.
In 2009, the U.S. Preventive Services Task Force changed its recommendation on screening exams for women aged 75 and older, noting that there was insufficient evidence to recommend for or against breast cancer screening in this population (Ann. Intern. Med. 2009;151:716-26).
However, the absence of evidence does not automatically translate into absence of benefit, Dr. Simon said in an interview. "You can’t assume that at 75, it’s not worth screening anymore. Yes, there’s no evidence from randomized trials of women older than 75, and the recommendations are based on this kind of evidence. But just because there are no trials doesn’t mean there is no benefit."
Dr. Simon and his coinvestigators extracted data from the 15-year Women’s Health Initiative study. The cohort comprised 9,057 women who had been diagnosed with breast cancer over a 12-year period.
The multivariate analysis examined the relationship between death from breast cancer and mammography screening intervals. The screening intervals studied were from 6 months to 1 year, 1 to 2 years, 2 to 5 years, and more than 5 years or never. The study cohort was divided into women by age: 50-74 years (6,497) and 75 years or older (2,560).
Baseline characteristics showed that the older group of women presented with dangerous breast cancers almost as often as did the younger group, including moderately differentiated (22% vs. 21%, respectively) and poorly differentiated tumors (28% vs. 31%). Older women were more likely to have hormone receptor–positive tumors (75% vs. 67%), and just as likely to have hormone receptor–negative tumors (12% of each group).
Stage was also similar between the older and younger groups: in situ (18% vs. 20%, respectively); localized (62% vs. 59%); regional (17% vs. 19%); and distant (1% in both groups).
Significant differences occurred when the investigators broke the group of more than 9,000 women out by mammogram intervals.
Overall, an interval of 5 or more years between a woman’s last mammogram and breast cancer diagnosis was associated with advanced-stage disease in 23%, compared with 20% in women with an interval of 1 year or less – a statistically significant difference, which could affect large numbers of women, said Dr. Simon, head of the breast multidisciplinary team at Barbara Ann Karmanos Cancer Institute in Detroit.
"We also saw significantly more aggressive cancers that were hormone receptor negative in the group with the longest interval between mammograms," he said (22% vs. 16%).
The multivariate analysis adjusted for age at enrollment in the WHI study and the trial component in which subjects enrolled, age at diagnosis, race and ethnicity, insurance and marital status, comorbidities, and body mass index at baseline.
In this analysis, women aged 75 years and older who went at least 5 years between mammograms were 67% more likely to die from a breast cancer than were those who had yearly exams. Older women who went 5 or more years between mammograms were three times more likely to die than were those who had yearly screening, Dr. Simon said.
The results show a need for stronger emphasis on regular mammograms for older women, he said. "Women are living longer and living vitally longer. If we have a test that can identify an early cancer ... we should take advantage of it."
For women of any age, mammograms have their downsides, including anxiety while waiting for results, overdiagnosis, and treatment of indolent, in situ tumors that may never progress to serious cancers – especially in women with a shorter lifespan ahead of them. Dr. Simon said those risks are small compared with the benefit of finding and treating a potentially lethal tumor.
Cost, however, is the sticking point, admitted Dr. Simon, who is also a public health expert.
"Resource allocation is something we can’t ignore. We know that it takes 1,700 mammograms to benefit one woman. That sounds like a lot, but when you think about it in a global perspective – how many women there are in this country – you see it in a different light. What we’re paying for mammograms is small potatoes."