By IHC and immunoblotting, STP tumor cells showed strong expression of nuclear TFE3, the canonical TFE3 target GPNMB, as well as expression of melanocytic and lysosomal markers (PMEL, MelanA and Cathepsin K) commonly upregulated in human MiT/TFE-related neoplasms (Fig. 2F, G). The gene discussed is CTSK; the disease is neoplasm.