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/Latina 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 self-reported as members of an Indigenous American community from the Andean Mountain region (indigenous subgroups: Quechuas, Aimaras, N=232) or the Amazonian region (indigenous subgroups: Shipibo-Konibo, Awajún, Ashaninka, Kichua, Ese Eja, Harakbut, Amahuaca, Shawi, Yanesha, Kakataibo, Nomatsigenga, N=71). We compared the distribution of age at diagnosis and tumor characteristics by region. 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.

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 (53.0% vs. 41.7% stage III or IV, P value=0.107) and more frequently with triple-negative tumors compared to women from the Mountain Region (30% vs. 16%, P value =0.115).

Conclusion: Differences between Indigenous American women from the Amazonian and Mountain Range regions in Peru could be due to variation in genetic predisposition to particular subtypes of the disease, variation in environmental exposures, as well as to differences in cancer awareness and access to care between the different groups. The more we learn by analyzing diverse populations, subpopulations and revealing heterogeneity within Latin American women, the better equipped we will be to provide adequate care for all women.

Citation Format: Lizeth I. Tamayo, Tatiana Vidaurre, Jeannie N. Vásquez, Sandro Casavilca, Jessica I. Palomino, Monica Calderon, Garth H. Rauscher, Laura Fejerman. Breast cancer characteristics among Indigenous American women from Peru [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5275. doi:10.1158/1538-7445.AM2017-5275