Soluble Fas (sFas) is generated by alternative mRNA splicing and lacks a transmembrane domain, is thought to inhibit Fas-FasL binding and blocks Fas-mediated apoptosis.

sFas has been identified in the supernatants of activated human lymphocytes and in several tumor cell lines, including hepatoma, osteosarcoma, and T- and B-cell leukemias and lymphomas. Elevated levels of sFas have also been observed in the serum of patients with solid tumors and hematopoietic malignancies. The clinical significance of serum sFas levels has not yet been clarified. The production of sFas may be involved in the pathogenesis of malignant disease.