Background: Genomically basal-type breast cancer is a heterogenous subtype that occurs at higher frequencies in non-Caucasian patients. Triple negative breast cancer (TNBC) has been refined into distinct transcriptomic groups including the basal-like immunoactive (BLIA), basal-like immunosuppressed (BLIS), luminal androgen receptor (LAR), and mesenchymal (MES) subtypes. Here we report the distribution of triple negative subtypes in genomically basal cancers from Caucasian (CA), African American (AA), and Latin American (LA) patients and the association of clinical estrogen receptor (ER) status. Methods: The FLEX Registry (NCT03053193) is an ongoing, prospective study evaluating primary tumors from patients with stage I-III breast cancer who receive the 70-gene signature and 80-gene signature (80-GS) molecular testing and consent to clinically annotated full transcriptome data collection. This sub-analysis evaluated 143 80-GS Basal type tumors from patients with self-reported ethnicity (60 CA, 59 AA, 24 LA). TNBC subtypes BLIA, BLIS, LAR, and MES were derived using an adjusted version of the 80-gene centroid signature published by Burstein and colleagues (2015). Differences in clinical ER expression between ethnicities were assessed by Fisher’s exact test. Results: Basal indices from 80-GS were not influenced by patient ethnicity (one-way ANOVA, p = 0.182). The frequency of BLIA, BLIS, LAR, and MES subtypes did not vary significantly by ethnicity (Fisher’s exact test, p = 0.671). The majority of tumors in all ethnic groups were BLIS (67% CA, 75% AA, 63% LA), followed by BLIA (22% CA, 22% AA, 25% LA), with low frequency of LAR (5% CA, 1.7% AA, 8.3% LA) and MES (5% CA, 1.7% AA, 4.2% LA) subtypes. Nearly one third (31%) of Basal type tumors were defined by IHC as ER positive and were present in all TNBC subtypes (39% BLIA, 29% BLIS, 33% LAR, and 20% MES); ER receptor expression ranged from 1-90% and was not associated with specific basal subtype (p = 0.8) nor ethnicity (P = 0.76). Progesterone receptor expression ranged from 1-50%. Conclusions: This analysis demonstrated that genomic Basal type tumor classification by 80-GS encompasses all TNBC subtypes evaluated regardless of ethnicity. Additionally, we show that IHC ER positive tumors occur in all TNBC subtypes assessed. These findings confirm the heterogeneous nature of basal breast tumors in CA, AA, and LA patients and highlight the clinical need to delineate basal biology in the ER+ cohort to advance treatment for basal-like tumors. Clinical trial information: NCT03053193.