D2-40: an additional marker for myoepithelial cells of breast and the precaution in interpreting tumor lymphovascular invasion.

D2-40 is a recently available mouse monoclonal antibody specific for human podoplanin and has been used in identifying lymphovascular invasion (LVI) of tumors. Although its expression has been evaluated in other tissues, its use as a marker for myoepithelial cells (MEC) of breast has not been studied. To explore its expression in the MEC of breast, paraffin-embedded tissue blocks from 48 patients with breast diseases were selected to include usual ductal hyperplasia (UDH, 41 cases), atypical ductal hyperplasia (ADH, 4 cases) and ductal carcinoma in situ (DCIS, 17 cases). Normal breast parenchyma and invasive carcinoma coexisting in the tissue sections were also included in the study. Immunohistochemistry for D2-40, calponin and p63 was performed and the staining patterns were reviewed and compared. D2-40 immunohistochemical staining is positive in the cytoplasm of MEC in UDH, ADH, and the majority of DCIS. The staining pattern of D2-40 is comparable with that of calponin, however D2-40 staining of MEC is weaker than that of calponin and with less background. In addition, myoepithelial cells and myofibroblasts at the edge of retraction spaces of DCIS are also stained by D2-40 that could be misinterpreted as tumor LVI. In conclusion, D2-40 immunohistochemistry reliably identifies the MEC of breast in a variety of lesions in a pattern similar to that of calponin and p63, and can be used as an additional MEC marker. Caution should be exercised when interpreting the staining of cells surrounding DCIS and carcinoma with retraction artifact.