Melanoma chondroitin sulfate proteoglycan (MCSP) is a cell-surface antigen expressed early in melanoma progression. It has been found to be involved in the spreading, invasion, and migration of human melanoma. MCSP influences melanoma behavior via the activation of the Cdc42 GTPase and phosphorylation of p130Cas. MCSP also activates signaling cascades involving FAK and ERK1/ERK2. In addition to its expression in melanoma cells, MCSP is also found in breast carcinomas, gliomas, neuroblastomas, and acute leukemias. MCSP is being considered as a target antigen for cancer immunotherapy.