An optimized small peptide drug candidate targeting epithelial mucin (MUC1) with antineoplastic activity. MUC1-targeted peptide GO-203-2C interacts with oncoprotein MUC1 C-terminal subunit on the cell surface, thereby impeding cell-cell interactions, signaling, and metastasis. MUC1 antigen, a membrane bound glycoprotein expressed by most glandular and ductal epithelial cells, is over-expressed in many diverse human carcinomas including those of the breast, prostate, lung, colon, pancreas, and ovary, and has been associated with poor prognosis.