Triple-negative breast cancer (TNBC) is an aggressive type of breast cancer in which calpain system plays an important role in its cellular processes including apoptosis and proliferation. Although such roles have been assessed in tumor pathogenesis, the correlation of its expression to the proliferating/apoptotic index has not been studied yet. Immunohistochemical staining of calpain-1 was performed on paraffin-embedded tissues to correlate its expression with clinicopathological variables and outcome. The proliferation activity was determined by calculating the percentage of cells expressing the Ki-67 antigen. The apoptotic index was assessed morphologically and biochemically using Haematoxylin & Eosin method and Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay, respectively. Calpain-1 was significantly expressed in TNBC tissues varying from low to high with a significant correlation to lymph node status but not with the other clinicopathological variables, suggesting its role as a prognostic factor. In addition, a positive correlation was found between both apoptotic counts assays (P<0.001, r=0.547) as well as with proliferation (P=0.045). Calpain-1 expression had no significant correlation with either proliferation (P=0.29) or apoptotic indices (P=0.071 and P=0.100). Determining calpain-1 expression may provide relevant prognostic value for TNBC cancer patients.
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