More women age 67 years and older diagnosed with DCIS or stage I breast cancer and women age ≥ 80 years diagnosed with stage II disease die of cardiovascular disease than breast cancer. Women age 67 years and older diagnosed with DCIS or stage I breast cancer are no more likely to die in the next 10 years than women without breast cancer. However, older women diagnosed with stage II disease or higher are at greater risk of mortality than women not diagnosed with breast cancer. When deciding on breast cancer screening, older women and their clinicians must weigh the risk of detecting breast cancers that may not affect life expectancy with the possibility of finding an aggressive breast cancer early.
Consistent with Diab et al,15
we found that women age 67 and older with stage I disease (lymph node-negative tumors, ≤ 2 cm) had survival similar to or better than women without breast cancer. We further found that older women with stage II disease had worse survival than controls; however, in the study by Diab et al,15
some of these women would have been classified as having lymph node–negative breast cancer and would have been found to have similar or better survival compared with the general population.
Unlike Diab et al,15
we additionally examined the impact of DCIS on older women's breast cancer survival. We found that older women diagnosed with DCIS or stage I disease had slightly lower mortality than controls, which may be a result of a healthy user effect.16,25
To account for this bias, we adjusted our models for mammography use, comorbidity, and health care utilization. Importantly, women diagnosed with DCIS or stage I breast cancer visited primary care with similar frequency to controls (mean visits, 7.0 visits for patient cases and 6.9 visits for controls) and had similar comorbidity (64.4% of patient cases had no Charlson comorbidities compared with 61.1% of controls). If there is a mortality risk for DCIS or stage I breast cancer among women age 67 years and older, the risk is likely low and not strong enough to counterbalance a healthy user effect. Additionally, our findings may be explained by the fact that women diagnosed with early-stage breast cancer may seek more medical attention after diagnosis, allowing for earlier diagnosis and treatment of other diseases and improved overall survival. Our data can be used to reassure women age 67 years and older diagnosed with DCIS or stage I breast cancer (particularly those receiving standard treatment) that their diagnosis is unlikely to significantly affect their life expectancy. Our data also suggest that older women diagnosed with early-stage breast cancer should be counseled about their cardiovascular risk factors because many will die from cardiovascular disease.
Women who received standard treatment for stage I breast cancer had better survival than controls, whereas those who did not receive standard treatment had similar or worse survival than controls. These data suggest that some older women in good health benefit from being diagnosed and treated for stage I breast cancer, preventing progression to more advanced disease, which is clearly associated with worse survival. We also found a dose response to treatment, suggesting that older women be offered standard treatment for early-stage disease.
This study has important limitations. Women with breast cancer may have differed from their controls in ways for which we do not have data (eg, functional status, tobacco use). It is plausible that some controls were misclassified as not having breast cancer. However, because we excluded potential controls if they had claims indicative of breast cancer since 1986, the only ways controls could be misclassified is if they were diagnosed with breast cancer before 1973 (when SEER began) or were somehow not captured by SEER between 1973 and 1985. If any of these women died of breast cancer, they would have been captured in SEER via death certificates. We performed sensitivity analyses to determine the extent to which misclassification of 1% to 2% of our controls would alter our findings (because 1.3% of the control pool had claims for breast cancer after 1985) and found no change in point estimates.
Additionally, data on socioeconomic status were community level rather than individual level; however, studies demonstrate moderate associations between individual and aggregate socioeconomic characteristics.24
American Joint Committee on Cancer staging changed in 2003, which may limit the generalizability of our findings. The greatest change in the staging system was that women with four or more positive lymph nodes are now categorized as having stage III rather than stage II disease.26
We repeated our analyses excluding women with four or more positive lymph nodes from stage II, and our aHR decreased from 1.2 to 1.1 but remained statistically significant. Although we found that women who received standard treatment were more likely to have breast cancer documented as the cause of death than women who received nonstandard treatment, standard treatment was not associated with an increased odds of death as a result of breast cancer (adjusted odds ratio, 1.1; 95% CI, 0.9 to 1.3) after adjustment for all covariates and tumor characteristics, suggesting that the elevated unadjusted risk was likely a result of confounding by indication. Finally, we were unable to match 1.4% of women diagnosed with breast cancer to a control. However, because we matched the oldest women diagnosed with breast cancer first, those who did not match were more likely to be younger than 75 years old but were otherwise similar to women who did match on other important characteristics including race/ethnicity, comorbidity, and proxies for income and education.
Overall, survival for women age 67 years or older diagnosed with DCIS or stage I breast cancer is slightly better than survival for women not diagnosed with breast cancer. However, survival is worse for older women diagnosed with stage II disease or higher compared with women not diagnosed with breast cancer. When discussing mammography screening, clinicians should inform older women that mammography may commonly detect breast cancers that will not affect their survival but may also find an advancing breast cancer early. Older women's life expectancy and comorbid diseases should be routinely factored into mammography screening decisions.