Our findings show racial/ethnic differences in breast cancer subtype according to menopausal status. It is well established that there are racial/ethnic disparities in breast cancer prognosis in Hawai’i. Loo et al. showed that the Native Hawaiian (NH) population experiences the poorest survival for both localized and advanced stage breast cancer of all racial/ethnic groups in Hawai’i and suggested that these poor outcomes may be due to biological factors [3]. Given these findings, it was expected that NH women would be more likely to have more aggressive breast cancer subtypes such as TN breast cancer. However, our data reveals that both premenopausal and postmenopausal NH women are more likely to have the hormone positive (ER+/PR+/HER2-) subtype rather than TN. Loo et al. found that NH women had a significantly higher incidence of hormone positive (ER+/PR+/HER2-), triple positive, and HER2+ breast cancer subtypes, compared to White women, but a significantly lower risk for the TN subtype, which is consistent with the results of our study [3]. These findings suggest that the poor outcomes that Native Hawaiian women with breast cancer experience may be due to factors other than subtype.
Conroy et al. conducted a multiethnic cohort study to examine the differential impact of obesity as a comorbidity on breast cancer survival. They showed that NH women with invasive breast cancer were more likely to have comorbidities such as obesity and cardiovascular disease compared to White, Japanese American, and Latino women. Compared to all other ethnic groups studied, obese NH women had a higher risk for all-cause mortality but a lower risk for breast cancer-specific mortality [5]. Another study conducted by Maskarinec et al. showed an inverse relationship between breast cancer-specific mortality and type 2 diabetes mellitus among NH women with invasive breast cancer [6]. They suggest that this may be due to the fact that NH women are more likely to have regular health visits for comorbidities and thus more likely to have early screening for breast cancer [6]. Nevertheless, these collective findings and the results of our study suggest that outcomes of NH women with breast cancer are multifactorial in nature.
Our findings show that premenopausal Japanese women are less likely to have the triple positive breast cancer subtype, which is consistent with findings in California-based studies that Japanese women were found to have lower rates of triple positive and TN breast cancer [7, 8]. In Hawai’i, Japanese women were found to have higher incidence rates of HR+ breast cancer compared to Whites, but Japanese women have lower 5-year mortality rates than White and NH women [3]. Japanese women in Hawai’i were also found to have a sharp increase in incidence of breast cancer which exceeds that of Whites but Japanese women have maintained relatively low mortality rates [3]. Improved clinical outcomes within this population may be directly attributed to higher incidence of the molecular subtypes associated with better outcomes, which may also be associated with higher rates for localized stage at diagnosis and smaller mean tumor size compared to other racial ethnic groups [3, 5]. Diagnosis at less advanced stages of disease may be due to non-biological factors including access to and frequency of screening, and lower prevalence of comorbidities may play a role in clinical outcomes within this patient population.
Postmenopausal Filipino women were significantly more likely to have HER2+ breast cancer compared to Whites. This finding is consistent with California-based studies [7, 8]. Loo et al. also found that Filipino women with HER2+ breast cancer breast cancer have poor 5-year survival rates compared to other racial/ethnic groups in Hawai’i [3]. These collective findings suggest that subtype may be a driving factor for clinical outcomes among postmenopausal Filipino women as these patients tend to have a poor prognosis, as measured by five-year survival for invasive breast cancer, compared to Japanese and White women [3].
We evaluated a significant number of new breast cancer cases from two major health systems in Hawaii. We recognize this is not a complete representation of our state based on the Hawaii Tumor Registry which reports an annual average number of new breast cancer cases of ~1,200 (Hawaii Tumor Registry-HTR, 2012-2016). In addition, there are other pathologic features that may contribute to clinical outcomes beyond subtype including grade, stage and treatment, which were not captured in this data review. Future studies evaluating these additional risk factors are underway and may help to further illuminate our understanding of the disparities we see.