Podoplanin expression in basal and myoepithelial cells: utility and potential pitfalls.

Podoplanin, D2-40, is often used for highlighting lymphatics. However, it has been described in a variety of normal and neoplastic tissues. We evaluated the expression of D2-40 in breast, salivary gland, skin, and mucosa, all organs rich in myoepithelial cells and basal cells. This study assessed the utility of using D2-40 to highlight basal/myoepithelial cells and to identify potential pitfalls in misinterpretation of lymphatic invasion. Our results showed that myoepithelial cells in breast and salivary gland and basal cells in prostate consistently demonstrate D2-40 immunoreactivity, but typically less intensely than lymphatics. Cutaneous and mucosal-based basal cells also have D2-40 expression, but often in a patchy, focal manner. In addition, many salivary gland tumors and squamous cell carcinomas had strong D2-40 expression, sometimes making distinction of lymphatics versus tumor edge staining difficult. D2-40 is excellent for assessing lymphatic invasion in breast, prostate, and cervix as long as the pathologist is aware of the expression in myoepithelial cells/basal cells to avoid misinterpretation of ductal carcinoma in situ or normal prostate glands or tumor stroma retraction as tumor lymphatic invasion. Given the patchy positivity in basal cells of skin and mucosa and the reactivity in squamous cell carcinoma, D2-40 was not helpful in assessing for microinvasion of squamous cell carcinoma.