Factors associated with prolonged time to treatment failure with fulvestrant 500 mg in patients with post-menopausal estrogen receptor-positive advanced breast cancer: a sub-group analysis of the…

Hidetoshi Kawaguchi, Norikazu Masuda, Takahiro Nakayama, Kenjiro Aogi, Keisei Anan, Yoshinori Ito, Shoichiro Ohtani, Nobuaki Sato, Shigehira Saji, Toshimi Takano, Eriko Tokunaga, Seigo Nakamura, Yoshie Hasegawa, Masaya Hattori, Tomomi Fujisawa, Satoshi Morita, Miki Yamaguchi, Hiroko Yamashita, Toshinari Yamashita, Yutaka Yamamoto, Daisuke Yotsumoto, Masakazu Toi, Shinji Ohno

The JBCRG-C06 Safari study showed that earlier fulvestrant 500 mg (F500) use, a longer time from diagnosis to F500 use, and no prior palliative chemotherapy were associated with significantly longer time to treatment failure (TTF) among Japanese patients with estrogen receptor-positive (ER+) advanced breast cancer (ABC). The objective of this subgroup analysis was to further examine data from the Safari study, focusing on ER+ and human epidermal growth factor receptor-negative (HER2-) cases. The Safari study (UMIN000015168) was a retrospective, multicenter cohort study, conducted in 1072 patients in Japan taking F500 for ER+ ABC. The subanalysis included only patients administered F500 as second-line or later therapy (n = 960). Of these, 828 patients were HER2-. Multivariate analysis showed that advanced age (≥65 years; p = 0.035), longer time (≥3 years) from AMBC ABC diagnosis to F500 use (p < 0.001), no prior chemotherapy (p < 0.001), and F500 treatment line (p < 0.001) were correlated with prolonged TTF (median 5.39 months). In ER+/HER2- patients receiving F500 as a second-line or later therapy, treatment line, advanced age, no prior palliative chemotherapy use, and a longer period from ABC diagnosis to F500 use were associated with longer TTF.