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Editor's Corner

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Invasive ductal carcinoma of the breast demonstrating cellular labeling for vimentin expression. This breast cancer sample does not express the p21 (WAF1/CIP1) cyclin dependent kinase inhibitor by immunohistochemistry analysis. The study by Bachman et al. demonstrates that the presence or absence of p21 can act as a “molecular switch” in the growth response to the cytokine Transforming Growth Factor-beta, Type 1 (TGF-beta). Breast epithelial cells that express p21 have a growth inhibitory response to TGF-beta. Conversely, breast epithelial cells devoid of p21 expression use TGF-beta as a growth stimulatory cytokine leading to an epithelial to mesenchymal transformation hallmarked by the decreased expression of E-cadherin and the increased expression of the cytoskeletal protein vimentin.