ST18 (suppression of tumorigenicity 18), also known as ZNF387 ((zinc finger protein 387), is a 1,047 amino acid nuclear protein that is expressed at low levels in heart, liver, kidney, skeletal muscle, pancreas, testis, ovary and prostate. Containing six C2HC-type zinc fingers and an SMC domain, ST18 is a repressor protein that binds to DNA sequences containing a specific bipartite element. ST18 is considered a transcription factor that represses basal transcription activity from target promoters and Inhibits colony formation in cultured breast cancer cells.