Differential Expression of Phospho-S6 in Hair Follicle Tumors: Evidence of Mammalian Target of Rapamycin Pathway Activation

The study investigated the expression of phospho-S6, a marker of mTOR pathway activation, in various benign and malignant hair follicle tumors. A total of 76 cases were analyzed, including fibrofolliculomas, trichoepitheliomas, tricholemmomas, pilomatricomas, malignant proliferating tricholemmal tumors, tricholemmal carcinomas, and trichoblastic carcinomas. Results showed that all malignant tumors exhibited strong and diffuse phospho-S6 staining in 70% to 90% of tumor cells. In contrast, benign tumors showed less frequent and more patchy phospho-S6 staining. The findings suggested that phospho-S6 is differentially expressed in benign versus malignant hair follicle tumors, indicating mTOR pathway activation is more prominent in malignant cases.