PD-L1 Expression in Carcinosarcomas of the Gynecologic Tract: A Potentially Actionable Biomarker.

Background: Carcinosarcomas of the gynecologic tract, also known as malignant mixed Miillerian tumors, are aggressive neoplasms with a high recurrence rate and poor prognosis. Despite advances in adjuvant therapies in recent years, the prognosis of these tumors has not improved. In fact, there are currently no consensus guidelines for the treatment of these neoplasms and the search for targetable biomarkers has not been successful so far. Programmed death-ligand 1 (PD-L1) has emerged as a potential target for therapeutics in a number of malignant tumors, including melanoma, lung, and colorectal cancer. In normal conditions, PD-L1 is thought to promote immune homeostasis via a number of pathways, but mainly through downregulation of cytotoxic T cells. In some human neoplasms, however, overexpression of PD-L1 by tumor cells has been observed, which can modulate the immune system to allow cancer cells to evade host response. As this marker could potentially be a therapeutic target for these tumors, the immunohistochemical expression of PD-L1 in a group of carcinosarcomas was evaluated in the present study. Material and Methods: Twenty-nine cases of gynecologic carcinosarcomas were analyzed, corresponding to tumors originating from the uterus (25), ovary (2), fallopian tube (1), and pelvic epithelium (1). Immunohistochemistry for PD-L1 was performed on paraffin sections and the staining results were assessed semiquantitatively in both epithelial and mesenchymal components of each tumor. Results: Positive membranous staining for PD-L1 was detected in 25/29 tumors (86%). The epithelial components were strongly positive in 19/29 (65%) and weakly positive in 6/29 tumors (21%). The mesenchymal elements were strongly positive in 8/29 (27%) and weakly positive in 3/29 tumors (10%). With exception of 1, all tumors with positive sarcomatous components had staining of the carcinomatous element. Four tumors were negative for PD-L1 in both components. Conclusions: This study shows that PD-L1 is expressed by the majority of carcinosarcomas, predominantly in the epithelial components. This is particularly important as most locoregional recurrences and distant metastases are of epithelial origin. This finding may serve as a basis for possible therapeutic approaches using antibodies that have already shown significant value in a number of other malignant tumors.