Elevated soluble Fas (sFas) levels in nonhematopoietic human malignancy.

Fas is a widely expressed membrane-anchored protein that induces apoptosis. Soluble Fas (sFas), generated by alternative mRNA splicing, can antagonize cell-surface Fas function. We have investigated sFas in 104 cancer patients with nonhematopoietic malignancies using a Fas-specific ELISA and immunoprecipitation. Our studies demonstrate an elevated 40-42-kDa sFas species in both patient serum and tumor explants. These observations provide the first evidence that sFas is increased in patients with solid tumors in a manner reflective of disease stage and tumor burden and argue that sFas can be synthesized and released both systemically and locally within the tumor microenvironment.