TBXAS1 and breast cancer: Aspirin intake has been associated with a lower risk of breast cancer incidence and mortality in epidemiological studies10–14 and pharmacokinetic data strongly suggest that aspirin might target COX-1 as well as its downstream pro-thrombotic TXA2 biosynthesis.15, 16 Recently, thromboxane A2 synthase 1 (TBXAS1) polymorphism was reported to be associated with breast cancer susceptibility.17 These findings prompted us to examine whether the TXA2 pathway functionally mediates breast tumorigenesis, and to clarify the underlying mechanism(s) of action.