BACKGROUND: Carcinosarcomas of the gynecologic tract, also known as malignant 
mixed Müllerian 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.