Immunolabeling pattern of podoplanin (d2-40) may distinguish basal cell carcinomas from trichoepitheliomas: a clinicopathologic and immunohistochemical study of 49 cases.

When the morphologic distinction between basal cell carcinomas (BCCs) and tichoepitheliomas is unclear, it poses a rare diagnostic challenge as the commonly defined histologic criterion is insufficient for differentiating these two neoplasms from each other. Their distinction is clinically important because the risk of progressive disease in BCC can be problematic, and trichoepitheliomas misinterpreted as BCC burdens the patient with an inaccurate diagnosis and consequential inappropriate surgery. Podoplanin (D2-40) is a well-known lymphatic endothelial surface marker that has been postulated to be upregulated in the outer root sheath of hair follicles and cutaneous neoplasms, such as adnexal tumors, squamous cell carcinomas, etc. We studied the expression of D2-40 by immunohistochemistry to determine if this marker could reliably differentiate these neoplasms from each other. A total of 49 cutaneous tumors, including 22 cases of trichoepitheliomas and 27 cases of BCC were examined. Of the 27 cases of BCC, 18 cases were located in the head and neck area, 5 on upper extremities, and 4 on the back. Of the 22 cases of trichoepitheliomas, all were from the head and neck area. D2-40 expression was present in 21/22 cases of trichoepitheliomas; 11 cases were diffusely positive (50%), 10 cases were focally positive (45.5%), and 1 case was negative (4.5%). D2-40 expression was present in 6/27 cases of BCC; 2 cases were diffusely positive (7.4%), 4 cases were focally positive (14.8%), and 21 cases were negative (77.8%). In summary, D2-40 expression was only weakly and focally positive in BCC (22.2% of cases) and diffusely and weakly positive in trichoepitheliomas (95.5% of cases). The sensitivity and specificity of D2-40 immunoreactivity to separate trichoepitheliomas from BCCs was 95.5% and 77.8%, respectively. This data suggests that D2-40 expression could be a useful potential marker to distinguish BCCs from trichoepitheliomas, especially when there is a high index of histologic suspicion for either of these two tumors. Our results also suggest that BCC can show differentiation toward the outer root sheath of hair follicles.