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Effect of endocrine therapy with tamoxifen on hormone receptor status in patients with breast cancer.
J Clin Oncol 27, 2009 (suppl; abstr e11598)
Background: Endocrine therapy (ET) of patients with hormone receptor (HR)-positive breast cancer (BC) is thought to adversely affect the HR status of the tumor with time. In order to evaluate this, a study was undertaken comparing the HR status of patients with estrogen receptor (ER)-positive BC prior to adjuvant tamoxifen (Tam) therapy and after progression. Methods: A retrospective analysis of all BC patients presented to the unit between 1999 to 2004 with an initial stage I-III ER-positive BC, who received Tam between 6 and 60 month and went on to develop progressive disease in the form of local recurrence or distant metastasis. Progression was confirmed by tumor biopsy and analysis of the HR status. All patients were evaluated for ER and progesterone receptor (PR) status using immunohistochemistry as well as tumor grading prior to Tam therapy and after relapse. Results: 67 eligible patients with ER-positive BC were recorded. All patient and tumor characteristics, including age, tumor size, histology and adjuvant therapy were similar as published elsewhere. 82% were initially PR-positive. The mean duration of Tam administration of 20mg po was 40.7±19.9 month. The mean duration to progression was calculated at 54.9±34.6 month. After relapse, 70.1% of tumors retained a positive ER status and only 53% showed positive PR expression. Using the nonparametric McNemar's test, a highly significant reduction (p< 0.001) of both HR was the result of Tam administration. Conclusions: our data suggests that progression under ET shows a trend towards loss of HR status (ER as well as PR). Therefore, this data is a useful tool for the clinician in evaluating the effectiveness of further ET in patients with progressive BC without having been able to confirm the present HR status through biopsy. Furthermore, as opposed to common belief, the reduction in positive ER tumors showed no correlation with tumor grading.