The S100A2, which is a protein in humans also known as CaN19, has an expression that's reduced in many cancers along with being down-regulated in melanoma.
S100 calcium-binding protein A2 (S100A2) is a protein that in humans is encoded by the S100A2 gene and it is located on chromosome 1q21 with other S100 proteins. S100A2, also known as CaN19 or S100L was first isolated from bovine lung tissue. Its expression is reduced in many types of cancer, thereby distinguishing the cancerous expression profile of the other proteins of the S100 group. It has been reported that S100A2 is downregulated in lung, kidney, prostate cancer and melanoma. 
