Abstract and Introduction
Abstract
Objectives To prospectively examine how age and comorbidity affect screening mammography use, cancer detection, and overall survival.
Design Prospective, with median follow-up of 10.2 years.
Setting A population-based cohort of Vermont women with data in the Vermont Breast Cancer Surveillance System.
Participants Women aged 70 and older with no history of breast cancer (N = 20,697).
Measurements Rates of screening, diagnostic procedure use, and breast cancer diagnosis were examined according to age and comorbidity. The effect of breast cancer on overall survival was assessed in relation to detection mode, tumor characteristics, and treatment.
Results Screening declined 9% per year after age 70 and 18% with each unit increase in comorbidity score, with corresponding increases in clinically detected breast cancer. Invasive cancer was associated with greater overall mortality (screen detected: hazard ratio (HR) = 1.22, 95% confidence interval (CI) = 1.07–1.40; clinically detected: HR = 1.68, 95% CI = 1.43–1.96). The latter HR reflects a much greater absolute risk of death for women in a population with high baseline mortality. Use of breast-conserving surgery as the only treatment for Stage I cancer increased markedly with age and was associated with shorter overall survival than radiation or mastectomy (relative risk = 2.23, 95% CI = 1.42–3.47).
Conclusion Lower screening mammography use by older women is associated with more clinically detected breast cancers, which are associated with poorer survival. Treatment received for early-stage cancer influences the effect of screening on survival.
Introduction
There is limited evidence regarding the effects of screening mammography in older women, but its benefits are generally thought to diminish as age and comorbidity reduce life expectancy. For example, in 2009, the U.S. Preventive Services Task Force (USPSTF) projected that the benefits of screening would be smaller for women aged 70 and older than for younger women and would decrease with age. The USPSTF also postulated that the harm of screening mammography "increases dramatically after about age 70 or 75 years" because women are likely to be diagnosed and treated for breast cancers that would never have become clinically apparent.
Studies to assess the effects of screening mammography in older women have primarily focused on tumor characteristics and outcomes in women diagnosed with breast cancer. Their results have generally shown that older women with early-stage breast cancers do not have greater mortality than controls or the general population. This might indicate that screening detects cancers that do not affect the survival of most older women, but such an interpretation assumes that similar survival would have been observed if the cancers had not been detected at an early stage.
To gain insight into the utility of screening mammography for older women, it was evaluated in the context of a general population, rather than only in women diagnosed with breast cancer. This was accomplished by prospectively examining mammography use and its effects in a historical cohort of women aged 70 and older with no prior diagnosis of breast cancer. The potential harms (diagnostic imaging in the absence of cancer, benign biopsy, diagnosis of in situ cancer) and benefits (early diagnosis and treatment of invasive cancer, better survival) of screening were assessed in relation to a woman's age and comorbidity.