ST7 (Suppressor of Tumorigenicity 7), also known as RAY1, TSG7 and FAM4A1, is a type I transmembrane protein belonging to the LDLR (low density lipoprotein receptor) superfamily and is designated LRP12 (1‑3). The mouse ST7 cDNA encodes 858 amino acids (aa) including a 32 aa signal sequence, a 460 aa extracellular domain (ECD) containing two CUB domains and five LDLR class A domains, a 21 aa transmembrane domain, and a 345 aa cytoplasmic domain containing motifs implicated in endocytosis and signal transduction (1, 2). Mouse ST7 shares 97% aa sequence homology rat, and 95% with human, bovine, equine and porcine ST7 within the ECD. A mouse ST7 splicing variant lacks aa 27‑45, and another potential variant has an alternate start site at aa 188. ST7 is widely expressed in normal tissues, especially on fibroblasts (1, 4). Highest mRNA levels are detected in heart and skeletal muscle (1). ST7 was originally proposed to be a tumor suppressor protein, but it is not consistently down‑regulated in a variety of cancers, either by mutation or loss of heterozygosity (1, 4‑7). In certain cancers, expression may even be up‑regulated (8). Expression may be associated with down‑regulated expression of extracellular matrix molecules that are involved in remodeling, such as SPARC, IGFBP5 and several matrix metalloproteinases, and modulation of in vivo tumorigenicity (4, 5).