Changes to the hormone receptor expression in patients treated with either tamoxifen or aromatase inhibitors as endocrine therapy for breast cancer

Abstract

10543 Background: Endocrine therapy (ET) of patients with hormone receptor (HR)-positive breast cancer (BC) is thought to adversely affect the HR expression of the tumor with time. In order to evaluate this, a study was undertaken comparing the HR status prior to adjuvant Tamoxifen (Tam) therapy and after progression in estrogen receptor (ER)-positive BC patients. Similarly, ET with aromatase inhibitors (AI) was investigated by comparing the HR status prior to AI therapy and after progression in ER-positive metastatic BC patients. Methods: A retrospective analysis of all stage I-III ER-positive BC patients who presented to the department between 1999 to 2004 and received adjuvant Tam for ≥ 6 month and had the tumor relapse (local recurrence or distant metastasis) confirmed by tumor biopsy. All patients were evaluated for ER and progesterone receptor (PR) status prior to ET as well as after relapse using immunohistochemistry. Similarly, stage IV ER-positive metastatic BC patients who received AI for ≥ 3 month with tumor biopsy prior and after AI therapy, were also analyzed in regards to their HR expression. Results: 44 eligible ER-positive BC patients constituted the Tam group. After relapse, 55% of the patients remained ER-positive, while 45% lost their positive ER status. For PR, 34 out of 44 patients were initially receptor positive (77%). Similarly, 15 out of 34 patients retained a positive PR expression (44%) and the 10 PR-negative patients showed no change in receptor expression following Tam. 5 eligible patients with ER-positive metastatic BC constituted the AI group. After progression, 4 out of 5 patients remained receptor positive, while 1 patient lost ER expression. For PR, 3 out of 5 patients were initially PR positive. After AI, only 2 patients showed a positive PR status. 2 patients were PR negative before and after AI therapy. Conclusions: Contrary to the belief that clinical progression under ET is probably as a result of the loss of HR expression, our data suggests that progression under ET does not necessarily result in the loss of HR expression. In fact, 55% of relapses under Tam and 80% of the progressions under AI remain ER positive, indicating potential susceptibility to other endocrine therapeutic agents. No significant financial relationships to disclose.