S100A2 is a member of the subfamily of S100 Ca2+-binding proteins, characterized by two distinct EF-hand structural motifs. It is a homodimeric protein that upon binding of calcium undergoes a conformational change (1). The S100A2 protein has been first detected in lung and kidney and is mainly expressed in a subset of tissues and cells such as breast epithelia and liver (2- 4). Interestingly the cDNA coding for the S100A2 protein was identified as a novel tumor suppressor gene by subtractive hybridization between normal and tumor derived human mammary epithelial cells (5). Expression studies showed that the S100A2 gene is markedly down-regulated in several tumor tissues of various origins like melanomas (6) and breast carcinoma (7). Moreover, growth factors were reported to alter the S100A2 gene expression at late G1/S-phase, indicating that S100A2 is cell cycle-regulated (8). Site-specific DNA methylation of the S100A2 gene promoter region in normal versus tumorigenic breast cancer cell lines indicated repression of gene expression in tumor cells, thus suggesting a role for S100A2 in suppression of tumor cell growth and possibly inhibition of tumor progression (7). By contrast, S100A2 overexpression was recently found to correlate with prognosis in ovarian, gastric, and lung cancers (9-11). Taken together, the role of S100A2 in carcinogenesis remains controversial.