Mast cell burden and immunophenotype of Chinese patients with cutaneous mastocytosis: a 10-year study with focus on the easily neglected pathogenic features.

Background: Cutaneous mastocytosis (CM) is a heterogeneous disease. Challenges remain in the detailed pathological features and pathogenic factors and their potential correlation in Chinese patients. Objective: This study aimed to characterize the pathological features and immunophenotypes of different CM subtypes in a real-world cohort and to explore the potential correlations between mast cell-related pathogenic features and clinical phenotypes. Methods: A cohort of 88 patients diagnosed with CM by histopathological examination in the Department of Dermatology between 2015 and 2024 was established. Immunohistochemical and clinicopathological analyses were performed. Results: Mast cell burden is associated with CM subtype, with the lowest burden being in telangiectasia macularis eruptive perstans (TMEP), followed by urticaria pigmentosa (UP) and diffuse CM/mastocytoma. High mast cell burden may also be associated with specific clinical morphology (e.g., elevated lesions) and an earlier age of onset. Different clinical subtypes exhibit distinct immunophenotypes. The expression of CD2, CD25, and CD30 may correlate with specific subtypes with high mast cell burden and provide potential value for CM diagnosis and subtyping. TMEP showed pathological differences from other subtypes, particularly in mast cell burden and immunophenotype. Conclusion: Different CM subtypes display distinct mast cell burdens and immunophenotypes, suggesting potential diagnostic value. The diverse clinical phenotypes may be associated with different mast cell burdens. TMEP may represent a unique and rare morphological variant of UP.