Factors associated with prolonged overall survival in patients with postmenopausal estrogen receptor-positive advanced breast cancer using real-world data: a follow-up analysis of the JBCRG-C06 Safari study.

Background: Assessing survival risk is important for discussing treatment options with estrogen receptor-positive (ER+) advanced breast cancer (ABC) patients. However, there are few reports from large-scale databases on the survival risk factors in ER+ ABC. The Safari study (UMIN000015168) was a retrospective, multicenter cohort study involving 1072 Japanese patients receiving fulvestrant 500 mg mostly as a second- or later-line endocrine therapy for ER+ ABC. The follow-up data after the Safari study were examined, focusing on any relationship between clinicopathological factors and overall survival (OS) in ER+ ABC patients.

Methods: OS in patients with ER+ ABC was analyzed by univariate and multivariate analyses with a Cox proportional hazards model in this study.

Results: A total of 1031 cases were evaluable for OS analysis. Multivariate analysis showed that younger age (< 60 years), longer time from ABC diagnosis to fulvestrant use (≥ 3 years), no prior palliative chemotherapy before fulvestrant use, and progesterone receptor (PgR) negativity (PgR-) were significantly correlated with prolonged OS (median 7.0 years). For cases with histological or nuclear grade data, lower histological or nuclear grades were also correlated with longer OS. In recurrent metastatic cases, long disease-free interval (DFI) was not correlated with longer OS.

Conclusions: In ER+ ABC patients whose treatment history included fulvestrant, younger age, longer time from ABC diagnosis to fulvestrant use, no prior palliative chemotherapy use, PgR-, and lower histological or nuclear grade correlated positively with prolonged OS.