Characterization of responders versus nonresponders to the anti-estrogen agent fulvestrant: A retrospective cohort study.

Abstract

117 Background: Patients with breast cancer often benefit from targeted endocrine therapy with estrogen receptor antagonists. However, the duration of therapeutic response to these agents is variable. We investigated several clinical variables that may potentially affect the duration of response to fulvestrant in the setting of metastatic disease. Methods: A retrospective cohort analysis was done in 137 patients who received fulvestrant between 2000 and 2011 at Moll Cancer Center at Fairview Hospital and Cleveland Clinic Cancer Center. Several patient variables e.g. degree of estrogen receptor positivity, BMI etc. were analyzed. The RECIST 1.1 criteria was used to measure disease activity. Clinical benefit (i.e., responsiveness) was defined as complete response, partial response or stable disease at 24 weeks of therapy. 57 patients had clinical benefit whereas 80 did not. The clinical variables were then compared between the two groups using Chi square test, Fisher's exact test and Wilcoxon’s rank sum test. A multivariable logistic regression model was then used to assess the association. Results: Patients who were responders exhibited a significantly higher proportion of bone and/or soft tissue only metastases than non-responders (51% vs. 24 %, p= 0.001). They also appeared to be older (mean age ± SD: 64.1 ± 12.2 vs. 60.2 ± 13.2, p=0.044) and had prior aromatase inhibitor sensitiveness (83% vs. 56, p=0.006). However, in multivariate and logistic regression analyses, the site of metastases was found to be the only significant predictor of response. Patients with bone and/or soft tissue only metastases were more likely to be responders than patients with visceral metastases (OR= 2.883 [95 % CI= 1.313 - 6.328], P= 0.012; OR: 3.325 [95% CI, 1.600-6.908], p=0.001, respectively). Conclusions: In metastatic breast cancer, patients with bone and/or soft tissue only metastases were more likely respond to fulvestrant therapy than those with visceral metastases.