Status of programmed death-ligand 1 expression in sarcomas.

BACKGROUND: Sarcomas are challenging to study because of their rarity and histomorphological complexity. PD1 and PD-L1 inhibitors showed a promising anti-tumor effect in solid tumors, where a relationship between PD-L1 expression and the objective response has been evidenced.

METHODS: In this study, we examined PD-L1 expression in 16 bone and soft tissue sarcoma cell lines of 11 different subtypes by means of western blot, flow cytometry and immunocytochemistry, and in 230 FFPE patient-derived tumor tissues by means of immunohistochemistry using three different antibody clones. The association between PD-L1 expression and clinicopathological features was evaluated.

RESULTS: We demonstrated that PD-L1 protein is highly expressed in pleomorphic rhabdomyosarcoma, fibrosarcoma, and dedifferentiated liposarcoma (DDLPS) cell lines. From the tissue microarray, undifferentiated pleomorphic sarcoma showed ≥ 1% immunoreactivity in 20%, 17.6%, and 16.3% of the cases with PD-L1 22C3, SP263, and SP142 antibodies, respectively. In whole sections stained with a PD-L1 22C3 antibody, DDLPS showed ≥ 1% immunoreactivity in 21.9% of the cases. In DDLPS group, cases with ≥ 1% PD-L1 expression showed statistically significantly worse recurrence-free survival (P = 0.027) and overall survival (P = 0.017) rates. Upon interferon-gamma treatment, the mRNA expression levels of PD-L1 were elevated in the HS-RMS-1, LIPO-224B, MLS1765, RH30, and RH41 cell lines.

CONCLUSIONS: We found that the expression of PD-L1 in sarcoma differs depending on the histologic subtype and the PD-L1 antibody clones. These results may serve as primary data for the selection of appropriate patients when applying PD1/PD-L1 inhibitor therapy in sarcoma.