A novel MAPK-microRNA signature is predictive of hormone-therapy resistance and poor outcome in ER-positive breast cancer

Purpose: Hyperactivation of ERK1/2 MAPK (hMAPK) leads to loss of estrogen receptor (ER) expression and poor outcome in breast cancer. microRNAs (miRNA) play important regulatory roles and serve as biomarkers of disease. Here, we describe molecular, pathologic, and clinical outcome associations of an hMAPK-miRNA expression signature in breast cancer. Experimental Design: An hMAPK-miRNA signature was identified, and associations of this signature with molecular and genetic alterations, gene expression, pathologic features, and clinical outcomes were determined in primary breast cancers from training data and validated using independent datasets. Univariate and multivariate analyses identified subsignatures associated with increased disease recurrence and poorer disease survival among ER-positive (ER⁺) patients, respectively. Results: High-hMAPK-miRNA status significantly correlated with ER-negativity, enrichment for basal and HER2-subtypes, and reduced recurrence-free and disease-specific survival in publicly available datasets. A robust determination of a recurrence signature and a survival signature identified hMAPK- miRNAs commonly associated with poor clinical outcome, and specific subsets associated more closely with either disease recurrence or disease survival, especially among ER⁺ cancers of both luminal A and luminal B subtypes. Multivariate analyses indicated that these recurrence and survival signatures significantly associated with increased risk of disease-specific death and disease recurrence in ER⁺ cancer and ER⁺ cancers treated with hormone therapy. Conclusions: We report an hMAPK-miRNA signature and two subsignatures derived from it that associate significantly with adverse clinical features, poor clinical outcome, and poor response to hormone therapy in breast cancer, thus identifying potential effectors of MAPK signaling, and novel predictive and prognostic biomarkers or therapeutic targets in breast cancer.