Merkel cell carcinoma in southern China: clinicopathologic and transcriptomic analysis with insights into an intraepidermal-predominant lesion

Merkel cell carcinoma (MCC) is a rare but highly aggressive primary cutaneous neuroendocrine carcinoma. Although its clinicopathologic and molecular features have been extensively studied in Western populations, data from Asian cohorts remain limited. We performed a retrospective clinicopathologic analysis of 10 MCC cases diagnosed in southern China and integrated RNA sequencing-based transcriptomic profiling in a subset of tumors. Conventional MCC cases displayed classic morphologic and immunophenotypic features, including dermal-based small blue cell tumors with cytokeratin 20 expression and neuroendocrine marker positivity. Transcriptomic analysis demonstrated clear separation between MCC tumors and matched normal skin, with enrichment of proliferative and cell cycle-associated programs, upregulation of neuroendocrine lineage-associated genes, and suppression of epidermal differentiation pathways. Notably, one case showed predominant intraepidermal growth with focal dermal invasion and exhibited a transcriptomic profile intermediate between normal skin and invasive MCC. Together with its morphologic, immunophenotypic, and clinical features, these findings support the possibility that intraepidermal-predominant MCC may represent an underrecognized early stage in the evolution of invasive disease. This study expands the clinicopathologic and molecular characterization of MCC in a low-incidence region and provides additional support for the biologic significance of intraepidermal-predominant lesions.