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Background: Cancer progression is a complex process consisting of a series of distinct steps. Cysteine proteases, such as cathepsins (Cts), are important molecules that play a central role in cancer progression and metastasis. Previous studies on human and mouse models of pancreatic cancer showed that both Cts B and Cts S are highly expressed in malignant tissues and the infiltrating macrophages. The aim of this study was to investigate the expression pattern of Cts B and S in human breast cancer tissues. Materials and Methods: Twenty-three formalin-fixed paraffin-embedded sections of breast cancer were stained for Cts B, Cts S, and CD206 using immunohistochemistry. Results: Cytoplasmic staining of Cts B and S was observed in tumor cells, endothelial cells, and macrophages. Cts B was preferentially expressed in breast cancer tissues by the different cells types. The majority of tumor samples were Cts B-positive in tumor cells, endothelial cells and macrophages (91%, 87%, and 70%, respectively) in comparison to Cts S (39%, 48%, and 57%, respectively; P < 0.001, P < 0.001 and 0.002). Correlation studies indicated significant relationships between the vascular and macrophage expression of Cts B (P = 0.01) and of Cts S (P = 0.03). However, neither Cts B nor Cts S expression in tumor cells correlated with other cell types (P > 0.05). Only the expression of Cts B in vascular endothelial cells correlated significantly with the tumor grade (P = 0.03). Conclusion: Results suggest that Cts B expression is more prominent than Cts S in breast cancer. Correlation studies imply different mechanisms regulating Cts B/S expression in tumor cells and other stromal components.
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