CTSK and hereditary clear cell renal cell carcinoma: Among the three most common fusions detected in TFE3-rearranged renal cell carcinoma, cathepsin K has been shown to be generally positive in PRCC-TFE3 rearranged renal cell carcinomas, variably expressed in SFPQ-TFE3 rearranged renal cell carcinomas, and negative in ASPCSR1-TFE3 rearranged renal cell carcinomas.