Eribulin mesylate is an inhibitor of microtubule dynamics that has been shown to prolong overall survival in patients with metastatic breast cancer. Recent studies have also reported that eribulin can reduce the abnormality of tumor vasculature by inducing remodeling the tumor microenvironment, and thereby reducing inner tumor hypoxia. As endocrine therapy has been reported to be ineffective under hypoxic conditions, and improved oxygenation of the peritumoral area may increase the sensitivity of endocrine therapy, “we hypothesized that endocrine therapy following eribulin administration might be more effective,” said Dr Kokoro Kobayashi of Tokyo, Japan. This study, Dr Kobayashi explained, was designed to evaluate the efficacy of endocrine therapy following eribulin treatment.
This retrospective study included 25 postmenopausal patients with metastatic breast cancer who had completed at least 2 endocrine therapies (treatment N-2 followed by N-1) prior to receiving eribulin, and at least 1 endocrine therapy (treatment N) after eribulin treatment. The time to treatment failure (TTF) and the effectiveness of the endocrine therapies on the basis of intraindividual changes were assessed.
In these 25 patients, the TTF of the endocrine therapy (treatment N-1) immediately preceding eribulin treatment was longer in 6 (24%) cases compared with the N-2 treatment. In contrast, the TTF of endocrine therapy (treatment N) after eribulin administration was longer than the N-1 treatment in 16 (64%) cases. Indeed, the TTF ratio between later endocrine therapy and earlier endocrine therapy was significantly higher (P = 0.018) when eribulin treatment occurred between the 2 therapies. Notably, this effect was not affected by drug selection for endocrine therapy.
Generally, the efficacy of late-line endocrine therapy is inferior to early-line endocrine therapy due to the accumulation of drug resistance in tumor cells. This study showed that eribulin treatment between 2 endocrine therapies prolonged the TTF in the majority of cases, supporting the hypothesis that eribulin may improve the sensitivity of endocrine therapy.