SASH1 is a 1247 amino acid protein that is significantly downregulated in the majority of primary breast tumor tissues, breast cancer cell lines, lung and thyroid tumors, as well as in certain colon carcinomas. It has been hypothesized that its expression is suppressed not due to mutation of the SASH1 gene, but instead via other mechanisms, such as promoter methylation. As a member of the SH3-domain containing expressed in lymphocytes (SLY1) gene family, SASH1 contains two sterile α modules (SAMs) and one Src homology-3 (SH3) domain, motifs that are predominantly found in adaptors, scaffold proteins and signaling molecules. Downregulation of SASH1 expression correlates with the formation of distant metastasis and is considered a negative prognostic parameter for patient survival.