Does mammography have benefit for older women with chronic illnesses?

Although breast cancer represents a major risk to older women, the benefit of screening mammography for women over 75 years is unclear. A recent study in The Journal of the National Cancer Institute aimed to determine the 10-year cumulative incidence of breast cancer versus death from causes other than breast cancer according to comorbidity and age in the Medicare-linked Breast Cancer Surveillance Consortium (BCSC).

The study included women between aged 66 to 94 years without a history of breast cancer who underwent screening mammography between 1999 and 2010. Participants were continuously enrolled in fee-for-service Medicare for 12 months before and after mammography. Information on breast cancer diagnoses and tumor characteristics was obtained by linking BCSC data to pathology services, regional Surveillance, Epidemiology, and End Results (SEER) programs, and/or state registries. 

For the study, the primary exposure of interest was the Charlson Comorbidity Index (CCI), which is a weighted index that predicts 1-year risk of death using Medicare Part B procedure and diagnostic claims data. CCI is calculated using the sum of weighted conditions and given scores of 1, 2, or 3 based on diagnoses with any of 16 disease conditions.  Primary outcomes of interest were incident breast cancer (invasive or dual carcinoma in situ [DCIS]) diagnoses and other cause death.

The study cohort included 222,088 women who were followed for a median of 107 months (interquartile range [IQR]: 65-120). Overall, participants were mostly white (84.8%), had a high school diploma or less (50.7%), reported no family history of breast cancer (82.5%), and had scattered fibroglandular density in their breast tissue (54.6%). By the end of follow-up, 7,583 women were diagnosed with invasive breast cancer and 1,742 were diagnosed with DCIS. Furthermore, 471 women died from breast cancer and 42,229 died from other causes. 

According to the study results, 10-year cumulative incidence of invasive breast cancer did not change with increasing CCI but actually decreased slightly with age: ages 66-74 [CCI0 = 4.0% (95% CI 3.9-4.2%) vs CCI ≥ 2 = 3.9% (95% CI, 3.5-4.3%)], ages 75-84 [(CCI0 = 3.7% (95% CI 3.5%-3.9%) vs CCI ≥ 2 = 3.4% (95% CI 2.9-3.9%)], and ages 85-94 [CCI0 = 2.7% ( 95% CI, 2.3-3.1%) vs CCI ≥ 2 = 2.1% (95% CI 1.3-3.0%)]. 

On the other hand, 10-year cumulative incidence of other causes of death increased with increasing CCI and age: ages 66-74 [CCI0 = 10.4% (95% CI, 10.3-10.7%) vs CCI≥2 = 43.4% (95% CI 42.2-44.4%)], ages 75-84 [CCI0 = 29.8% (95% CI, 29.3-30.2%) vs CCI≥2 = 61.7% (95% CI, 60.2-63.3%)], and ages 85-94 [CCI0 = 60.3%, (95% CI, 59.1-61.5%) vs  CCI≥2 = 84.8% (95% CI, 82.5-86.9%)]. 

The 10-year cumulative incidence of breast cancer death was small and did not vary by age.

The authors believe their findings suggest that cumulative incidence of other cause death was much higher than breast cancer incidence and death, although that varied by comorbidity and age. Therefore, older women with favorable life expectancies would benefit more from continued screening mammography than those with increased comorbidity.