Breast cancer characteristics (eg, tumor grade, histology, hormone receptivity) appear to be similar between women age ≥ 80 years and younger women. However, women age ≥ 80 years receive less aggressive treatment than younger women. Greater comorbidity likely accounts for some of the observed difference; however, among women with a Charlson score of 0, 26% of those age ≥ 80 years did not receive standard treatments (mastectomy or BCS + RT) for early-stage breast cancer compared with only 6% of younger women. We also found that the risk of dying from breast cancer increases significantly after age 80. Our findings suggest that we may be able to identify a subgroup of women age ≥ 80 years who may benefit from more aggressive work-up and treatment of their early-stage breast cancer. Conversely, we may also be able to identify a population of older women on the basis of tumor characteristics, comorbid diseases, and life expectancy who may not need as aggressive treatment. The majority of older women with early-stage disease died from other causes. Future studies are needed to develop tools that can help clinicians appropriately target breast cancer treatments to the oldest women most likely to benefit.
Despite prevailing opinion that breast cancer tumor characteristics are more favorable among older women than younger women, we generally did not find clinically important differences by age at diagnosis for most tumor characteristics. However, the youngest women in our study were older than most women included in other studies.25
It is possible that tumors present with more favorable characteristics with older age but beyond age 67 years, these differences are negligible. Other studies have also failed to show increases in hormone receptor positivity among women age 70 years and older.14,26
Although we and others27
have found that the proportion of women with positive lymph nodes increased with age, we also found that the proportion of women who had their lymph nodes examined declined substantially with age, which may reflect biased sampling. Clinicians may be choosing to sample only lymph nodes of older women who they suspect will be positive.
Regardless of age, we found that the majority of older women undergo surgery for treatment of breast cancer. Among women with stage I disease, BCS + RT is the most common treatment for women age 67 to 79 years. Mastectomy is the most common treatment for women age 80 to 84 years, which may reflect physicians' attempts to treat older women effectively but without radiation. After age 85, BCS alone is the most common treatment. Among women with stage II disease, mastectomy is the most common treatment for all women, regardless of age; however, BCS alone becomes substantially more common after age 80. Some of the oldest women may be undertreated, while others may be being treated appropriately. Future work should focus on identifying tumor and patient characteristics associated with an improved response to aggressive therapy among the oldest women.
As for the impact of RT on older women's breast cancer survival, we found that older women treated with BCS + RT had the best breast cancer survival. However, these women also had the best overall survival, suggesting that unmeasured factors related to survival affected treatment decisions. Clinical trials show that RT after BCS compared with BCS alone reduces breast cancer recurrence among older women with early-stage disease but does not affect survival.8,28,29
Since we found that breast cancer mortality increases significantly after age 80 and these women are the least likely to be treated aggressively, our findings suggest that some older women in good health may benefit from more aggressive treatment.
We found that treatment with chemotherapy was associated with a survival benefit for women age 67 to 79 years with ER-negative, lymph node–positive disease, results similar to those in other studies.6,7
However, chemotherapy tended to be associated with worse breast cancer survival among women age ≥ 80 years. Since few women age ≥ 80 years received chemotherapy, our findings suggest that chemotherapy is reserved for the oldest women with the worst tumor characteristics.
This study has several important limitations. Since this is an observational study, there is potential for selection bias and residual confounding by factors for which we do not have data, such as performance status, social support, and treatment with hormonal therapy. In post hoc sensitivity analyses, we examined the effect of an unmeasured confounder such as hormonal therapy on our estimated aHRs. Assuming that treatment with tamoxifen is more common among women age ≥ 80 years than among younger women30
and that the survival benefit of tamoxifen ranges from 10% to 50% reduction in breast cancer mortality,31
we found that our aHRs would decrease by less than 10% if we were able to adjust for tamoxifen use.32,33
Completion of death certificate data could also differ by age. However, studies have found that coding of cancer on death certificates is accurate, particularly coding of breast cancer death.34,35
In addition, administrative data may underestimate the prevalence of many chronic conditions. Moreover, we needed to exclude women who had missing claims data, the majority of whom had health maintenance organization coverage. Health maintenance organizations tend to include younger and healthier women, which may mean that our sample of women age 67 to 79 years may be older and in poorer health than the overall population. However, this would bias our comparisons between the oldest-old and younger-old toward the null. AJCC staging was modified in 2003 such that women with four or more positive lymph nodes are now classified as stage III. However, only 4.7% of women in our sample had four or more positive nodes. Changes in staging had no effect on women classified as stage I. Finally, although socioeconomic status data were community level, studies have demonstrated moderate associations between individual and aggregate socioeconomic characteristics.20
In summary, breast cancer characteristics are similar among women age ≥ 80 years and younger women. However, women age ≥ 80 years receive less aggressive treatment and are more likely to die from breast cancer. Future studies should focus on identifying tumor and patient characteristics that can be used to help target breast cancer treatments to the oldest women most likely to benefit.