Lower level of MAPK expression is associated with anthracycline resistance and decreased survival in patients with hormone receptor negative breast cancer.

INTRODUCTION: Hormone receptor negative breast cancer is encountered in about 30% of all patients with breast cancer and is considered as a prognostically unfavorable subset. The aim of this study is to evaluate the prognostic impact of various molecular markers in patients with receptor negative breast cancer.

METHODS: Tumor specimens from 140 patients with receptor negative (ER, PR) breast cancer were analyzed for MAPK, Her-2/neu, EGFR and PI3K expression by immunohistochemistry. The prognostic significance of these molecular factors, in addition to various prognostic variables were determined with respect to disease-free and overall survival.

RESULTS: Nineteen (13.6%), 45 (32.1%), 16 (11.4%) and 47 (33.5%) patients had positive staining for EGFR, PI3K, Her-2/neu and MAPK, respectively. Twenty-three patients with positive MAPK (16.4%) had a high level of expression (score 4-7) and 24 (17.1%) had a low score (1-3). A lower percentage of MAPK expression was significantly associated with a poorer OS (p = 0.03) and a tendency for shorter DFS (p = 0.08) among those who were positive for MAPK. Anthracycline resistance remained the only independent significant variable for OS by Cox regression analysis (p = 0.001, HR:26.1). In patients with recurrent disease, median survival after initial relapse was 16.8 months. MAPK was determined as the only prognostic factor for this endpoint. Patients with higher level of MAPK staining showed significantly shorter survival following initial recurrence (p = 0.04).

CONCLUSION: MAPK expression is a significant prognostic factor for non-metastatic patients with hormone receptor breast cancer. A lower level of staining is shown to be associated with with antracycline resistance and oveall survival, whereas a higher expression level is correlated with shorter survival following initial relapse, suggesting possible role of different molecular mechanisms pertaining to tumor progression once recurrence occurs. Further translational research is required to elucidate molecular mechanisms of the cross-talk between intracellular signaling and molecular pathways leading to drug resistance in patients with receptor negative breast cancer.