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Cathepsin B (CTSB)

Reviewer: Nat Pernick, M.D. (see Reviewers page)
Revised: 29 September 2012, last major update September 2012
Copyright: (c) 2002-2012, PathologyOutlines.com, Inc.


● Lysosomal cysteine protease associated with focal adhesions, inhibited by cystatin C, an endogenous cysteine protease inhibitor
● Usually acts only in cell cytoplasm, but in malignant tumors is secreted extracellularly and degrades extracellular matrix so tumor cells can invade
● Highest staining at invasive edge of tumor
● Acts as effector of invasion in HER2+ breast cancer (Mol Cell 2012;45:764), inflammatory breast cancer (Breast Cancer Res 2011;13:R115), prostate cancer (Int J Cancer 2012;131:2034)
● In gliomas, radiation treatment increases cathepsin B levels, suggesting that inhibition may be useful therapy (Neuro Oncol 2012;14:745, Mol Carcinog 2012 Apr 11 [Epub ahead of print])
● Inhibition may limit breast cancer metastases (Cancer Res 2012;72:1199)

Clinical features

● CSF levels increase with age (Neurol Sci 2012 Mar 23 [Epub ahead of print])
● Endosomal cathepsin B may play a functional role in activation of highly pathogenic Nipah virus (J Virol 2012;86:3736)

Uses by pathologists

● Cytoplasmic stain, but intense staining may appear nuclear
● High expression is poor prognostic marker in colon carcinoma, gliomas (Hum Pathol 2005;36:1008), lung cancer (serum levels, Oncol Lett 2011;2:693)

Micro images

Skin: normal

Breast: inflammatory carcinoma and breast cancer NOS

Colon cancer

Lung: nonsmall cell lung cancer-tumor associated macrophages

Prostate: benign and malignant

Salivary glands (minor) in patients with Sjögren's Syndrome (fig C/D)

Positive staining - normal

● Bowel, prostate, skin, thyroid; some endothelial cells

Positive staining - disease

● Various malignancies: breast, colon, lung, prostate carcinoma; glioma; melanoma (Pathol Res Pract 1999;195:171)

End of Stains > Cathepsin B

Ref Updated: 9/29/12

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