PD-L1 expression in invasive solid papillary breast carcinomas.

Abstract

Invasive solid papillary carcinomas (ISPC) are rare malignant neoplasms in the classification of WHO 2019 breast tumors. We aimed to investigate the correlations between programmed cell death ligand-1 (PD-L1) expression status of tumor and immune cells and clinicopathological parameters by molecular classification of this rare morphological subtype. This study will contribute to the literature about the PD-L1 expression state of ISPCs for the first time. The study included 19 invasive solid papillary carcinoma cases diagnosed between 2009 and 2019 in Pathology Department. Molecular subtyping was performed in 19 cases by immunohistochemical studies (ER/PR, Her-2/neu, Ki-67), and PD-L1 expression was evaluated in neoplastic and immune cells. PD-L1 expression was detected in 4 (21%) cases, 3 (75%) of them were in luminal B and 1 (25%) were in the luminal A group. The correlation between molecular subtypes and PD-L1 expression was statistically significant (P = 0.016). Patients with PD-L1 expression had a higher Ki-67 index than patients without PD-L1 expression (P = 0.037). In addition, there was a statistically significant correlation between PD-L1 expressions of intratumoral lymphocytes and PD-L1 expressions of neoplastic cells (P = 0.004). While predicting the group that will benefit more from immunotherapy in solid papillary carcinoma cases, not only PD-L1 expression of tumor cells but also PD-L1 expression in tumor infiltrating lymphocyte (TIL) can help. In addition, PD-L1 staining rates of tumor cells as well as clinicopathological parameters (molecular subtype, high Ki-67 index, presence of TIL) can be predictive about immunotherapy.