Association between up-regulation of Fas ligand expression and apoptosis of tumor-infiltrating lymphocytes in human breast cancer.

In order to study the significance of FasL expression in immune escape of breast cancer, FasL protein expression and the number of tumor-infiltrating lymphocytes (TILs) in 40 specimens of breast cancer were detected by immunohistochemitry. The expression of FasL mRNA was measured by in situ hybridization in the consecutive tissue slices of 40 breast cancers respectively. By using terminal deoxynucleotidyl transferase-mediaed dUTP nick end labeling (TUNEL), apoptotic cells were detected in 40 specimens of breast cancer. The expression of FasL was detected in all 40 specimens to varying degrees. In the consecutive tissue slices, the location of expression of FasL protein corresponded with that of FasL mRNA. In those with FasL extensive expression, the number of TILs was less (P<0.05), the apoptotic index (AI) of TILs was higher and the AI of tumor cells was lower (P<0.01) than those with FasL weak expression respectively. The AI of TILs was correlated with that of tumor cells (r= -0.629, P<0.01). In conclusion, breast cancer cells can induce the apoptosis of TILs through the expression of FasL, which can counterattack the immune system. This may be a mechanism of immune evasion in breast cancer.