Endocrine response after prior treatment with fulvestrant in postmenopausal women with advanced breast cancer: experience from a single centre

Abstract

The pure anti-oestrogen fulvestrant has now been licensed for use in advanced breast cancer which has progressed on an anti-oestrogen. Optimal sequencing of various endocrine agents becomes very important in the therapeutic strategy. We report our experience of further endocrine response with another endocrine agent after prior fulvestrant treatment. Among all patients with advanced breast cancer who had been entered into five phase II/III trials using fulvestrant as first- to ninth-line endocrine therapy in our Unit since 1993, 54 patients who fulfilled the following criteria were studied for their subsequent endocrine response: (i) oestrogen receptor positive or unknown; (ii) having been on a subsequent endocrine therapy for ≥6 months unless the disease progressed before; and (iii) with disease assessable for response according to International Union Against Cancer criteria. Eleven patients had received an aromatase inhibitor prior to fulvestrant, which resulted in five CBs (clinical benefit = objective remission/stable disease (SD)) for ≥6 months). Twenty-eight patients achieved CB on fulvestrant. They went on subsequent endocrine therapy with two partial responses, 11 SDs and 15 PDs (progressive disease) at 6 months. The median survival from starting fulvestrant and subsequent endocrine therapy was respectively 46.6 and 18.2 months. Among the remaining 26 patients who progressed at 6 months on fulvestrant, there were three SDs and 23 PDs at 6 months on subsequent endocrine therapy. The median survival from starting fulvestrant and subsequent endocrine therapy was respectively 12.5 and 9.3 months. Of all these 54 patients, 30% (n = 16) therefore achieved CB using another (second- to tenth-line) endocrine agent (anastrozole = 26; tamoxifen = 12; megestrol acetate = 11; others = 5). It would thus appear that further endocrine response can be induced in a reasonable proportion of patients after failing fulvestrant.