Serpin B5 is a secretive protein that belongs to the Serpin (Serine Protease Inhibitor) family and Ov-serpin subfamily. Serpin B5 is expressed in the prostate, testis, intestine, tongue, lung, and thymus. Serpin B5 exhibits no serine protease inhibitory activity. Serpin B5 also functions as tumor suppressor an angiogenesis inhibitor. It has been shown that Serpin B5 blocks the growth, invasion, and metastatic properties of mammary tumors. Furthermore, high expression of Serpin B5 is linked to squamous cell carcinoma in non-small-cell lung cancer.