Abstract B79: Breast cancer characteristics and survival among Indigenous American women from Peru

Background: Breast cancer prognosis depends on stage at diagnosis and varies by intrinsic tumor subtype. In the US, the distribution of intrinsic subtypes has been shown to differ between racial/ethnic groups with African American and Hispanic/Latina women more likely to be diagnosed with the more aggressive triple-negative breast cancer (TNBC) lacking expression of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2), compared to non-Hispanic/Latino White women. Hispanics/Latinos in the US are a heterogeneous group originating from different countries with different cultures and ancestral backgrounds. Information about the distribution of tumor subtypes in Latin American regions is lacking. Methods: Data for these analyses come from the Instituto Nacional de Enfermedades Neoplásicas (the Peruvian National Cancer Institute), which diagnoses and treats ~20% of all breast cancers diagnosed in Peru. We have abstracted data from clinical records for 303 patients diagnosed with breast cancer between 2010 and 2015 and who are members of Indigenous American communities from the Andean Mountain region (N=232) or the Amazonian region (N=71). We compared tumor characteristics and survival between the two groups. Comparisons between the two regions were conducted using chi-squared tests, as well as a t-test for age at diagnosis. Breast cancer subtype was defined as luminal A (ER/PR+/HER2-), luminal B (ER+/HER2+), HER2 overexpressing (ER/PR- HER2+), and triple-negative (ER/PR- HER2-) based on immunohistochemistry. Survival analyses were conducted using a Cox proportional hazards model and included region, age at diagnosis, stage, and tumor subtype as predictors. Results: Overall, tumors from the 303 Indigenous American women from Peru included in the present study were 37% luminal A, 20% luminal B, 23% HER2 overexpressing, and 19% triple-negative. Our analyses showed that women from the Amazonian region were diagnosed at a younger age (50 vs. 55 mean age at diagnosis, P value =0.001), later stage (61% vs. 48% stage III or IV, P value=0.06), and more frequently with triple-negative tumors compared to women from the Mountain region (31% vs. 17%, P value =0.013). Women from the Amazonian region had a 70% higher mortality hazard than the women from the Mountain region in a model adjusted by age at diagnosis (hazard ratio 1.73, 95%CI 1.06-2.86, p=0.027). In the full model including stage and tumor subtype, the difference i