Comprehensive Immunophenotypic Profiling and Prognostic Value in Salivary Gland Mucoepidermoid Carcinoma

To characterize the proliferative and immunophenotypic profiles of salivary gland mucoepidermoid carcinoma (MEC) and to explore their associations with clinicopathologic features, tumour microenvironment (TME) characteristics, Pan-TRK expression, and disease prognosis. Forty-one MEC cases were examined using immunohistochemistry for Ki-67, Cytokeratin 19 (CK19), Aquaporin 5 (AQP5), CD3, CD8, and Pan-TRK. Clinicopathologic parameters were correlated with protein expression patterns to assess tumour behaviour and potential TRK fusion activity. Elevated Ki-67 expression correlated with aggressive histologic features and poor clinical outcomes. CK19 expression was significantly reduced in high-grade (HG) MECs, and its loss was associated with unfavourable prognosis. High tumour-infiltrating lymphocyte density correlated with an increased risk, while cases with poor outcomes exhibited heterogeneous CD3⁺ and CD8⁺ T-cell profiles. Pan-TRK expression was detected in only five cases (12.2%), typically weak and heterogeneous, and no robust correlation with cancer recurrence risk was present. The heterogeneous immunophenotypic profiles observed in MEC reflect the biological complexity of the TME. Ki-67 was found to be a reliable indicator of tumour proliferative activity and an unfavourable prognosis. High Ki-67 expression, loss of CK19, and elevated TIL density were associated with increased recurrence risk. Although Pan-TRK expression was infrequent and not prognostically relevant, its occurrence in highly proliferative tumours suggests possible biologic interplay. Expanding immunophenotypic profiling to incorporate spatial analyses and single-cell–level characterization may deepen our understanding of MEC pathogenesis and support personalized therapeutic strategies.