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Cathepsin K is selectively expressed in the stroma of lung adenocarcinoma but not in bronchioloalveolar carcinoma. A useful marker of invasive growth.

Rapa I, Volante M, Cappia S, Rosas R, Scagliotti GV, Papotti M

Department of Clinical and Biological Sciences, University of Turin and San Luigi Hospital, Orbassano, Torino, Italy.

Lung bronchioalveolar carcinomas (BACs) are noninvasive tumors showing lepidic growth and excellent prognosis, whereas all the other variants of adenocarcinoma are invasive tumors with a worse prognosis. The identification of minimal invasive foci in adenocarcinoma, therefore, is of prognostic relevance. A series of 68 pulmonary tumors, including 40 acinar/papillary adenocarcinomas, 18 adenocarcinomas of the mixed subtype, and 10 BACs was tested by immunohistochemical analysis for cathepsin K expression, a proteinase involved in bone and extracellular matrix remodeling. Cathepsin K was produced by epithelial tumor cells in most invasive adenocarcinomas and, interestingly, by macrophages and fibroblasts in the stroma of invasive adenocarcinomas but not of BACs (P < .001). Our findings suggest pathogenetic implications of cathepsin K in the mechanisms of tumor invasiveness in lung carcinoma; in addition, cathepsin K immunodetection may be a valuable adjunct in the correct classification of pulmonary adenocarcinomas, especially in small sclerosing BACs and mixed adenocarcinoma subtypes with minimal infiltrative growth.

Published 12 May 2006 in Am J Clin Pathol, 125(6): 847-54.
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