Predictors of response to second-line endocrine therapy for breast cancer

This study reports on factors predicting response to second-line endocrine therapy in 250 patients with breast cancer for which they were assessable for response by the International Union Against Cancer (UICC) criteria. Clinical details relating to first-line endocrine therapy were available for all patients. We have not included in this study patients who received first-line endocrine therapy but did not or have not yet proceeded to second-line hormone therapy--e.g. died from rapidly progressive disease, started chemotherapy for rapidly progressive disease, or remained in long-term remission on first-line endocrine therapy. One hundred and fifty nine patients (72%) achieved remission (objective response and static disease [OR + SD]) on first-line endocrine therapy with a median duration of 19 months. For second-line endocrine therapy the remission rate was 53% (132/225) with a median duration of 15 months. Tumour grade and oestrogen receptor status of the primary tumour were shown to be independent predictors of response to second-line endocrine therapy while response to first-line endocrine therapy was a predictor of the duration of response to second-line endocrine therapy. In the sub-group of patients who showed OR or SD to both first and second-line therapies, there was no correlation between the time to progression (TTP) on first and second-line therapies.