ECT2⁺ cell group acts as cancer stem cell in malignant pleomorphic adenoma

Salivary carcinoma ex pleomorphic adenoma (CXPA) is a carcinoma that develops from benign pleomorphic adenoma, and it is characterized by aggressiveness and poor prognosis. Recent advancements in cancer stem cell (CSC) research have identified CSCs as critical contributors to tumor carcinogenesis due to their unlimited self-renewal ability. Single-cell RNA sequencing has enabled a comprehensive analysis of CSC heterogeneity. However, CSCs in CXPA remain largely unexplored. In this study, we constructed a comprehensive atlas of CXPA at single-cell resolution and demonstrated that CXPA exhibited intratumoral heterogeneity. We identified four tumor epithelial cell subgroups characterized by epithelial development, cell cycle, extracellular matrix remodeling, and salivary secretion signatures. ECT2⁺ tumor cells in the cell cycle cluster were identified as CSCs in CXPA. Analysis of tumor tissues from patients with CXPA revealed that ECT2 expression was strongly associated with invasiveness and prognosis. Targeting the ECT2 gene significantly inhibited tumor sphere formation and aggressiveness in CXPA cell lines. Our findings provide new insights into CXPA diversity and origin, with substantial clinical implications for targeting the ECT2 gene in CXPA treatment.