BerEP4 is widely expressed in tumors of the sweat apparatus: a source of potential diagnostic error

Background A 63-year-old man presented with an ulcerated nodule with a rolled pearly edge on his back. A punch biopsy showed diffuse strong BerEP4 expression and retraction artifact. Consequently the tumor was diagnosed as a basal cell carcinoma but on excision the tumor proved to be a porocarcinoma. Although Jimenez et al. reported BerEP4 expression in porocarcinoma, this result is not widely appreciated. This observation prompted us to investigate BerEP4 expression in sweat apparatus tumors. Methods Immunocytochemistry was performed using Dako monoclonal mouse BerEP4 with Ventana Benchmark XT immunostainer. Omission of the primary antibody served as a negative control. Results Fourteen of 26 porocarcinomas had at least focal BerEP4 expression and two were diffusely and at least focally strongly positive. Seven of seven chondroid syringomas stained diffusely positive, with strong ductal expression; the single chondroid syringocarcinoma was negative. Five of 6 poromas and two of two hidradenomas had focal expression, and staining particularly highlighted the ducts, a co-localization also apparent in the four spiradenomas and three cylindromas. The single primary mucinous carcinoma had diffuse strong BerEP4 expression. Discussion This case and pilot study shows that BerEP4 expression is common in these selected sweat apparatus tumors, and staining may be strongly so. This observation should be borne in mind in clinical practice.