Expression of Fas ligand in metastatic prostatic carcinoma: Suggestive of possible clonal expansion of subpopulation with metastatic potential

Fas ligand (FasL) is a type II transmembrane tumor necrosis factor family p rotein, known to trigger apoptosis in cells that bear the FasL receptor, Fa s. The authors found that normal prostate, benign hyperplasia, and most pro static carcinoma cells at the primary site did not express FasL, whereas me tastatic prostatic carcinoma cells in lymph nodes and bone marrow displayed almost uniform. immunohistochemically detectable. FasL expression. However , small foci of FasL-positive prostatic carcinoma cells amid a vast majorit y of FasL-negative tumor cells were noted at the primary sites in patients with distant metastases. Analysis of the FasL gene and its mRNA by polymera se chain reaction and reverse transcriptase-polymerase chain reaction, resp ectively, suggested that the expression of immunohistochemically detectable FasL in metastatic tumor cells was not due to mutation in the FasL gene wi th resulting overexpression. Further. FasL expression was detectable in the acinar epithelial cells of prostates with morphologic atrophic changes, su ggesting that FasL also plays a role in the physiologic apoptosis process o f noncancerous prostate. The current data suggest that a subpopulation of p rostate carcinoma cells clonally expresses FasL, and this subpopulation may have metastatic potential. Evaluation of FasL expression in the primary tu mor thus may provide a useful parameter for predicting metastatic potential of the tumor.