To characterize determinants of treatment outcome in a real world population of 161 post-menopausal hormone receptor-positive metastatic breast cancer patients treated with fulvestrant. Descriptive statistics for demographics, anthropometrics, clinical and molecular characteristic were compared across subgroups of sensitivity/resistance to prior endocrine therapy and tested in uni/multivariate models. Clinical benefit was more common in sensitive patients with higher estrogen receptor expression and when fulvestrant was given in first line (p=0.02 and 0.046). In resistant patients, PFS was longer with lower BMI (p=0.01). Among endocrine sensitive women, longer PFS was associated with fulvestrant in first-line, single metastasis and no visceral involvement (p=0.01, 0.003 and 0.01). OS was shorter in resistant patients with HER2-positive disease and if fulvestrant was given in second and subsequent line (p=0.03). In sensitive patients, we observed worse OS with multiple metastases (p=0.008). Multivariate analyses confirmed longer PFS in resistant patients with lower BMI and older age (p=0.002 and 0.007). OS in resistant patients was negatively influenced by HER2 positivity and fulvestrant in second and subsequent line (p=0.04). In sensitive women, multiple metastases were associated with poorer survival (p=0.002). This evidence encourages considering patient and disease characteristics in decision making and outcome interpretation for patients candidate to fulvestrant.
Keywords: endocrine resistance; endocrine sensitivity; fulvestrant; hormone receptor positive metastatic breast cancer.