In summary, in this large, diverse, population-based sample of women diagnosed with breast cancer between 2005 and 2007, we found no compelling evidence of adjuvant chemotherapy underuse among black or Hispanic women regardless of level of acculturation. In fact, Hispanics had statistically significantly higher odds of receiving chemotherapy than the other racial/ethnic groups after controlling for measurable factors. Low-acculturated Hispanics had the highest odds of receiving chemotherapy. These findings were contrary to our hypotheses and may be related to the types of facilities in which Hispanics receive specialty care. SES, measured via education attainment and income, and marital status were not associated with receipt of chemotherapy. With the exception of age and insurance, the only correlates of chemotherapy receipt were disease characteristics associated with a higher risk of distant recurrence and greater benefit of chemotherapy (higher stage, higher grade, negative hormone receptor status). Most patients who did not receive chemotherapy attributed omission to their physicians' recommendations (or perhaps their perceptions of physicians' recommendations).
The relationship between increasing age and decreasing use of chemotherapy () in our sample is consistent with previous research.69–72
Despite the fact that older women with a life expectancy of 5 or more years reap the same degree of risk reduction with chemotherapy as younger women,73,74
increasing age was an independent factor associated with chemotherapy receipt. Rates of chemotherapy receipt in our sample of older patients were higher than those in earlier time periods,69,70
suggesting that dissemination regarding the benefits of chemotherapy in otherwise healthy older patients is taking place. There is, however, additional room for improvement in the care of older women.75
The association between chemotherapy receipt and age among women younger than age 50 years is particularly notable. Although increasing age is associated with lower rates of chemotherapy receipt, as described, age has not been shown to play a role in receipt of chemotherapy in women younger than age 50 years. This novel finding suggests that in our sample, age was incorporated into chemotherapy decision making along the entire continuum of age. Unmeasured tumor features, such as HER2 positivity and presence of angiolymphatic invasion, have been shown to be more common in younger women in large, single-institution studies68,76
and may have been more common in our participants younger than age 50 years compared with older women. If present, such differences could account for the higher rates of chemotherapy receipt in the younger women in our sample.
The absence in our study of information on HER2 status and angiolymphatic invasion limits the ability to explain not only rates of chemotherapy among the younger patients but also the independent association between Hispanic ethnicity and chemotherapy receipt. HER2 status was not available in the SEER registries for patients in our sample. Treatment guidelines in place at the time our patients were diagnosed incorporated both HER2 status and the presence of angiolymphatic invasion (as a high-risk feature), and in fact, both features have been shown to predict use of chemotherapy in women with node-negative, estrogen receptor–positive disease.77
Higher rates of angiolymphatic invasion or HER2-positive disease have been identified in some76
but not all18
studies that included Hispanics. There is no evidence that HER2 status differs between black and non-Hispanic white women.18,78
We also identified an association between insurance status and chemotherapy receipt. Patients with insurance indicated as “other” most likely had private insurance, and these patients had higher odds of receiving chemotherapy compared with patients with Medicare; Medicaid insurance was associated with chemotherapy omission, as has been seen in other studies.47
In addition to lacking data on angiolymphatic invasion and HER2 status, there are several other limitations of this study. We did not have information on chemotherapy regimen, dose or dose-intensity, or rates of completion of chemotherapy. Previous work has shown that black women and women of lower SES are more likely to receive nonstandard, often single-agent, chemotherapy regimens79
and intentionally reduced doses of chemotherapy with the first cycle of chemotherapy.80
Others have shown that black women participating in clinical trials receive lower doses of chemotherapy over the course of their chemotherapy than white women.81
Thus, although we have demonstrated no differences in the rate of chemotherapy according to race/ethnicity, we cannot state that the quality of chemotherapy is equivalent across different patient subgroups.
Another limitation of this study is that our sample was drawn from only two regions in the United States and included only patients who speak English or Spanish, so we cannot necessarily generalize our findings to other regions or other patient groups. Wu et al45
recently demonstrated chemotherapy underuse according to area-level SES in seven state registries, whereas our study did not demonstrate SES disparities (using individual-level measures of SES). It is possible that the two regions we included in our study differ from care in those seven states in terms of urbanicity and availability of specialty cancer services. Finally, response bias may be playing a role in that those who participated in the study may differ in unmeasured ways from those who did not participate in the study.
In conclusion, it seems that race and ethnicity need not pose barriers to receipt of adjuvant chemotherapy. Such a finding is encouraging as we continue to address racial and ethnic disparities in the receipt of quality cancer care. Nonetheless, differences and disparities do exist in receipt of chemotherapy according to age, insurance, and employment status. These findings identify opportunities to continue to improve the quality of breast cancer care.