Hence, the title of this subheading, Cathepsin K and Tumors with an Altered mTOR Pathway, includes angiomyolipoma and pure epithelioid PEComa/epithelioid angiomyolipoma, eosinophilic solid and cystic renal cell carcinoma, and high-grade oncocytic tumor/sporadic renal cell carcinomas with eosinophilic and vacuolated cells/eosinophilic vacuolated tumors, which are all characterized by a dysregulation of the mTOR pathway and cathepsin K expression. The gene discussed is CTSK; the disease is angiomyolipoma.