Survivin (IAP4) is the smallest member of the Inhibitors of Apoptosis Protein (IAP) gene family. The IAPs are involved in multiple cell functions such as cell signaling, cell division, metabolism, and exhibits differential expression in nearly all human cancers, but not in most normal tissues. IAP family members usually contain multiple baculovirus IAP repeat (BIR) domains, but the Survivin gene encodes proteins with only a single BIR domain. Survivin is nearly undetectable in terminally differentiated cells, but found in most tumors including renal cell carcinoma, ovarian carcinoma, hepatocellular carcinoma, prostate carcinoma and breast carcinoma. Survivin expression is linked to tumor progression, but not patient survival. The overexpression of survivin in cancer may overcome this apoptotic checkpoint and favor aberrant progression of transformed cells through mitosis.