Expression Patterns of Hair and Epithelial Keratins and Transcription Factors HOXC13, LEF1, and β-Catenin in a Malignant Pilomatricoma: A Histological and Immunohistochemical Study

The study investigated a malignant pilomatricoma, revealing that it maintained hHa5/HOXC13 co-expression and disrupted hHa1/β-catenin–LEF1 expression in its transitional cell compartment, similar to benign pilomatricomas. However, unlike benign forms, the malignant tumor's transitional cells also strongly expressed epithelial keratins K5, K14, and K17. This expression pattern, along with the presence of numerous parakeratinizing whorls and absence of calcification, suggested a dominance of the epithelial differentiation pathway, potentially preventing the tumor's calcification.