131 Loss of PD-L1 expression in metastatic Merkel cell carcinoma strongly correlates with a poor prognosis

Abstract

Merkel cell carcinoma (MCC) is a rare, but highly malignant skin cancer. Despite its high malignancy, however, a good prognosis, including spontaneous regression, has been reported in some sporadic cases since the first report by O’Rourke and Bell in 1986. T-cell-mediated immunity is suggested to play an important role in tumor regression, and the expression of programmed death-ligand 1 (PD-L1) in cancer cells correlates with better clinical outcomes in MCC, in contrast to other solid carcinomas, such as malignant melanoma. To evaluate these immune responses, we collected 90 specimens from 71 patients with MCC from 9 facilities. The cohort included 26 men and 45 women (median age 77.27 years, range 40-98). Spontaneous regression occurred after biopsy in 6 cases. The heterogeneity of immune response factors, including PD-L1 expression, between primary and metastatic lesions in the same patient make it difficult to use them as prognostic factors. PD-L1 expression in primary lesions did not correlate with overall survival (r=0.068; 95% CI, -0.19 to 0.31; p=0.59). PD-L1 expression also did not correlate with the presence or absence of lymph node or distant metastasis. Once metastasis did occur, however, the PD-L1 expression strength in metastatic lesions was strongly correlated with overall survival (r=0.91; 95% CI, 0.70 to 0.97; p<0.0001). PD-L1 expression in metastatic lesions may directly reflect the host’s level of immune resistance at that point in time.