Friend or foe: ABCG2, ABCC1 and ABCB1 expression in triple-negative breast cancer

Background ATP-binding cassette (ABC) transporters are responsible for the efflux of a wide variety of anti-cancer agents and have been implicated in the chemoresistance of various solid tumors. Chemoresistance is a major cause of therapeutic failure, especially in the highly aggressive triple-negative breast cancer (TNBC) in which, unlike estrogen receptor-expressing (ER+) BC, both endocrine and targeted treatments are ineffectual. We aimed to investigate the level and frequency of expression of the three most important ABC transporter, ABCG2, ABCC1, and ABCB1, according to breast cancer subtype. Methods We evaluated ABCG2, ABCC1, and ABCB1 protein expressions in 124 primary breast tumors (78 samples were classified as TNBC, while 46 were classified as ER+) by immunohistochemistry and correlated it to clinicopathological characteristics and outcome. Results All three transporters had significantly higher expression and were more frequently expressed in TNBC compared to ER+ tumors ( p