Comparative analysis of PD-L1 expression and tumor-infiltrating lymphocytes in metaplastic breast carcinoma and gynecologic carcinosarcoma: A single-institution retrospective study

Metaplastic breast carcinoma (MBC) and gynecologic carcinosarcoma (GCS) are rare, clinically aggressive cancers that demonstrate epithelial components and mesenchymal or sarcomatoid components. In this study, we assessed PD-L1 expression and tumor-infiltrating lymphocytes (TILs) in MBC and GCS. Overall, PD-L1 positivity using the SP142 clone was seen in 50 % of MBC and 51.9 % of GCS cases, with PD-L1 expression in tumor cells significantly higher in MBC cases (p = 0.034), and PD-L1 expression in immune cells similar in MBC and GCS cases. PD-L1 expression was significantly higher in epithelial components than in mesenchymal components in both MBC and GCS cases (p = 0.0005). TILs were low in the majority of MBC and GCS cases (≥ 10 %) and generally correlated with PD-L1 expression; however, many PD-L1 positive cases with low TILs were seen. PD-L1 expression using the 22C3 clone was additionally assessed, with positivity seen in 62.9 % of MBC cases and 30 % of GCS cases. Concordance between SP142 and 22C3 results was seen in 62.5 % of MBC cases and 80 % of GCS cases. Overall, our findings suggest that a subset of MBC and GCS cases may benefit from immune checkpoint inhibitor therapy. Our findings also illustrate unique aspects of PD-L1 expression patterns in these tumors which may harbor additional prognostic and therapeutic significance.