Cathepsin K

Author: Nat Pernick, M.D. (see Authors page)

Revised: 18 November 2015, last major update July 2013

Copyright: (c) 2003-2015,, Inc.

PubMed Search: cathepsin k
Definition / General
  • Lysosomal, papain-like cysteine protease with high matrix-degrading activity; expression is driven by microphthalmia transcription factor (MITF) in osteoclasts
  • Responsible for bone resorption and remodeling
  • Germline mutations cause sclerosing osteochondrodysplasia pycnodysostosis, a rare autosomal recessive skeletal dysplasia characterized by abnormal bone and tooth development
Uses by Pathologists
  • Diagnosis of renal angiomyolipoma and other renal erivascular epithelioid cell tumors (Mod Pathol 2012;25:100)
Micro Images

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Bone: osteoclasts in osteoclastoma and normal

Intervertebral disc

Maxillary sinus: basaloid squamous cell carcinoma

Images hosted on


Kidney: perivascular epithelioid cell tumors

Kidney: TFE3 gene fusion carcinomas

Kidney: other renal cell
carcinomas are Cathepsin K-

Lung: lymphangio-leiomyomatosis

Skin tumor - melanoma

Skin tumor - other

Positive Staining - Normal
Positive Staining - Disease
Negative Staining