Trichoepithelioma: a 19-year clinicopathologic re-evaluation.

Accurate histopathologic distinction between trichoepithelioma (TE) and basal cell carcinoma (BCC) may be challenging. From 97 cases diagnosed as TE during the period 1979-1997, 73 available cases were studied with regard to: 1) stroma; 2) retraction effect; 3) papillary-mesenchymal bodies (PMB); 4) amyloid; 5) mitotic figures; 6) apoptotic cells; 7) inflammation; 8) granuloma; and 9) calcification. A judgment was made regarding diagnosis. The patients' medical records were subsequently reviewed for clinical features and possible recurrence. The diagnosis of TE was confirmed histologically in 48 (65%) of 73 cases. Fifteen cases (21%) were reclassified as BCC (RC-BCC), eight other cases (11%) were reclassified as other lesions, and two additional cases (3%) could not be confidently classified as either TE or BCC. The most helpful differentiating features were the presence of retraction effect (in 100% of RC-BCC vs. 37% of TE), myxoid stroma (in 80% of RC-BCC vs. 12% of TE) and PMB (in 20% of RC-BCC vs. 81% of TE). Unexpected findings in TE were detection of amyloid in 33%, apoptotic cells in 100%, and mitotic figures in 46%. Five of the 15 RC-BCC have recurred (33%), whereas there have been no recurrences in the confirmed TE group. A constellation of histopathologic criteria may help to discriminate problematic examples of trichoepithelioma from basal cell carcinoma.