Sinonasal mucosal melanoma (SNMM) is a rare and aggressive malignancy, with many clinically relevant characteristics yet to be fully explored and integrated into treatment strategies to improve patient outcomes. Cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4, CD152) plays a pivotal role in suppressing anti-tumor immunity and contributes to the development of an anti-inflammatory tumor microenvironment (TIME). In this publication, we aim to explore the expression of CTLA-4 in SNMM to better understand the potential for applying anti-CTLA-4 antibodies in the treatment of this rare malignancy and give insights into CTLA-4 expression as a predictive marker patient survival. This is particularly relevant for patients who cannot be cured by surgery, as more than half of SNMM cases are diagnosed at advanced stages (cT4a or cT4b), with local invasiveness or metastasis. We focus on standardized methods for CTLA-4 assessment, providing meaningful insights into the CTLA-4 status of the affected tissue through an immune cell (IC) score, which is already established for other well-known ICIs and has been part of FDA approvals already. In this way we pursue our goal to support the implementation of modern therapeutic regimens to improve patient prognosis and clinical outcomes. In addition, patient data was collected, including age, sex, symptoms, side, specific localization, histological type, melanin distribution, lymph node metastases, distant metastasis, invaded surrounding tissues, AJCC stage and OS. The results of the histological CTLA-4 examinations are currently pending.

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