498P Impact of estrogen receptor expression on real-world effectiveness of first-line ET+CDK4/6i in patients with HR+/HER2- advanced BC. - Vernieri, C.; Dieci, M.V.; Caputo, R.; Vigneri, P.; Giuliano, M.; Curigliano, G.; Toss, A.; Botticelli, A.; Pedersini, R.; Cinieri, S.; Lambertini, M.; Tagliaferri, B.; et al. (Annals of Oncology, 2025)