Absent progesterone receptor expression in the lymph node metastases of ER-positive, HER2-negative breast cancer is associated with relapse on tamoxifen.

AIMS: Progesterone receptor (PR) expression is prognostic in early stage breast cancer. There are several reports of discordant expression between primary tumour and axillary lymph node (ALN) metastasis expression of oestrogen receptor (ER) and PR. We sought to determine whether expression of these biomarkers in the synchronous ALN metastases of ER positive (+), HER2 negative (-) breast cancer could provide more accurate prognostic information.

METHODS: The retrospective cohort included 229 patients from a single institution with ER+, HER2- breast cancer who had synchronous ALN metastatic disease (2005-2014). PR expression was correlated with relapse-free survival, and subset analysis was performed for patients who received adjuvant tamoxifen or an aromatase inhibitor.

RESULTS: One patient had an ER+ primary tumour, which was ER- in the ALN metastasis. 27 (11.3%) were PR- in the primary tumour and 56 (23.6%) in the ALN metastasis. The predominant change was from PR+ in the primary tumour to PR- in the lymph node. Absence of PR expression in the ALN was significantly associated with relapse; however, this was not the case in the primary tumour. In a subset analysis of patients taking adjuvant endocrine therapy, poorer prognosis was limited to those with PR- metastases on tamoxifen (HR=5.203, 95% CI 1.649 to 16.416, p=0.005). No significant prognostic effect of PR- metastases in patients taking aromatase inhibitors was seen (HR=1.519, 95% CI 0.675 to 3.418, p=0.312).

CONCLUSIONS: Evaluation of PR expression in ALN metastasis may enable prediction of patients who are less likely to benefit from adjuvant tamoxifen. This study should be replicated in other cohorts.