Problems in Diagnosis of Proliferating Tricholemmal Cystic Carcinoma


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View Figure  		Fig. 12A–C  Proliferating tricholemmal cystic carcinoma. This cystic neoplasm "shelled out" when an incision was made above and down to it. Moreover, it is encompassed by epithelium like that of a cyst whose lining resembles that at the isthmus and at the base of a follicle advanced in catagen. This constellation of findings could lead a histopathologist to a wrong diagnosis of a proliferating tricholemmal cyst, as was the case for decades. In actuality, this is a proliferating tricholemmal cystic carcinoma that, almost certainly, took origin from an isthmic-catagen (tricholemmal) cyst.

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View Figure  		Fig. 13A–C  Proliferating tricholemmal cystic carcinoma. The shape of this subcutaneous cystic neoplasm telegraphs that it "shelled out" during the course of the surgical procedure performed to remove it. That finding, in itself, usually implies a neoplasm is benign. But this particular type of carcinoma is the exception to the rule. It often "shells out" because it is circumscribed so sharply and its border is so smooth. Those two attributes give credence to the idea that a proliferating tricholemmal cystic carcinoma like this one developed in a tricholemmal (isthmus-catagen) cyst.

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View Figure  		Fig. 14A–C  Proliferating tricholemmal cystic carcinoma. The lesion is cystic in the sense that it is a well circumscribed, epithelium-lined enclosure that houses cells, but it is not a true cyst because of the extensive proliferation of epithelial cells, which makes it a neoplasm. Because it "shelled out" and cornified cells of it have calcified, the neoplasm could be inferred incorrectly to be benign. In actuality, this is a proliferating tricholemmal cystic carcinoma by virtue of its silhouette, nuclear characteristics, and differentiation.