Patients diagnosed with basal-like breast cancer face a more aggressive disease course and more dismal prognosis than patients diagnosed with luminal A and luminal B breast cancer molecular subtypes (1-4). We mined published microarray data (5, 6) to understand in an unbiased fashion the most distinguishing transcriptional features of tumors from patients with basal or basal-like subtype breast cancer. We observed transcriptome-wide differential expression of Rho-associated

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... g protein kinase 2, ROCK2, when comparing tumors of patients with basal-like breast cancer with that of other PAM50 molecular subtypes. ROCK2 mRNA was present at significantly higher quantities in the tumors of patients with basal-like breast cancer. Analysis of patient survival data revealed that ROCK2 primary tumor expression was correlated with overall survival in luminal B subtype breast cancer. Elevated ROCK2 expression appears to distinguish basal-like human breast cancer from the other molecular subtypes.