Background: “Triple negative” has been used to characterize a subtype of breast cancer that lacks estrogen, progesterone, and HER2 receptor expression. They are aggressive cancers with limited treatment options. It’s unknown if similar phenotype found in other cancer types, like endometrial cancer, harbor similar molecular alterations and prognosis. We aim to compare molecular features between TNEC and TNBC. Methods: A total of 3133 endometrial cancer samples were evaluated by Caris Life Sciences (Phoenix, AZ) from Mar, 2011 to Jul, 2014 by multiplatform profiling, which included a combination of sequencing (Sanger or NGS), protein expression (IHC), and/or gene amplification (CISH or FISH). 545 TNEC and 2049 TNBC were identified based on reported pathology and compared using Fisher exact tests. Results: Compared to an incidence of 15-20% TNBC in breast cancer, 17% (545/3133) TNEC was seen in our cohort, of which 13% were endometrioid, 22% serous, 26% carcinosarcoma, 7% clear cell, and 22% other. Compared with TNBC, TNEC showed 1.9 exonic mutations per case while TNBC showed 1.2 mutations per case. As shown in the table, AR expression is lower in TNEC than TNBC. TP53 mutation was common in both but more frequent in TNBC. While BRCA1/2 mutation rates were similar, low MGMT and ERCC1 were more common in TNEC, suggesting increased aberrant DNA repair. DNA synthesis protein expression was higher in TNEC including TS, RRM1, and TOPO2A, although TNBC had higher TOPO1. PD-1 expression was more common in TNEC suggesting immune pathway involvement. PI3K/AKT/mTor, MAPK and Wnt pathways were more involved in TNEC with greater PTEN, PIK3CA, FBXW7, KRAS and CTNNB1 mutations. Conclusions: Our study reveals significantly higher overall mutation rates in TNEC than TNBC, and specifically higher activations of multiple molecular pathways including PI3K/Akt/mTor, MAPK and Wnt. Further studies are warranted to validate these findings in clinical trials.