Stereotypical Examples of Proliferating Tricholemmal Cystic Carcinomas


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View Figure  		Fig. 2A–C  Proliferating tricholemmal cystic carcinoma. This huge neoplasm extends from beneath the epidermis to far into the subcutaneous fat. Despite the vertical orientation, sharp circumscription, and smooth border, it is malignant because of its asymmetry, marked variation in size and shape of aggregations, and tendency of aggregations to confluence. The cytopathologic features are those of carcinoma, namely, crowded, large, pleomorphic nuclei. The cytoplasm shows signs of cornification abnormally. It is likely that this proliferating tricholemmal cystic carcinoma began in an isthmic-catagen cyst.

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View Figure  		Fig. 3A–B  Proliferating tricholemmal cystic carcinoma. At scanning magnification, the silhouette could be misconstrued as that of a benign neoplasm, especially because the lesion has "shelled out" partially consequent to a space having formed between compressed fibrous tissue contiguous with the epithelial component of the neoplasm at its base and what was normal subcutaneous fat, and as a result of an epithelial lining similar to that of a cyst which encompasses it nearly completely. Within the cystic structure, both solid and cystic elements can be discerned. The components are interconnected and associated with innumerable orthokeratotic corneocytes. The lining epithelium simulates that of a follicular cyst of isthmic-catagen type. This is a carcinoma, however, because it is asymmetric, aggregations vary markedly in size and shape, and aggregations have become confluent in many zones, sometimes assuming peculiar geometric outlines. Cytopathologically, the findings are those of a carcinoma, the nuclei being crowded and pleomorphic. It is a proliferating tricholemmal cystic carcinoma because differentiation is toward outer sheath at the isthmus. It is reasonable to infer that this proliferating tricholemmal cystic carcinoma originated in an isthmic-catagen cyst.

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View Figure  		Fig. 4A–B  Proliferating tricholemmal cystic carcinoma. This neoplasm could be misinterpreted as being benign because it "shelled out" partially during the surgical procedure designed to remove it. That this truly is a malignant neoplasm can be told by study of the silhouette and the cytopathologic attributes. Within the asymmetric neoplasm, aggregations are crowded and vary markedly in size and shape. Nuclei of neoplastic cells are crowded and pleomorphic. This is a specific type of carcinoma, namely, one that differentiates toward outer sheath at the isthmus. Such a carcinoma probably began in an isthmus-catagen cyst.

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View Figure  		Fig. 5A–C  Proliferating tricholemmal cystic carcinoma. At first glance with scanning magnification, the topographic features of this neoplasm could convey a sense of benignancy: it "shelled out" and its border is smooth. In actuality, the entire neoplasm is a carcinoma. The epithelium itself resembles that of normal outer sheath at the isthmus, that finding signifying differentiation of the carcinoma toward "tricholemmal sheath" at the isthmus. At higher magnifications, the neoplastic cells, particularly at the periphery of aggregations, can be seen to be crowded, have strikingly atypical nuclei, and be accompanied by mitoses. Some aggregations have a jagged periphery. In short, this type of carcinoma with tricholemmal differentiation at the isthmus is designated properly proliferating tricholemmal cystic carcinoma.

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View Figure  		Fig. 6A–C  Proliferating tricholemmal cystic carcinoma. This neoplasm situated in the subcutaneous fat is malignant because it is asymmetric and poorly circumscribed, and aggregations that constitute it are made up of cells whose nuclei are crowded and atypical. It is a carcinoma because neoplastic cells are cohesive. The silhouette is characteristic of proliferating tricholemmal cystic carcinoma. The prominent cornification in the form of large zones of parakeratosis and of many dyskeratotic cells are expected findings in that particular type of carcinoma.

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View Figure  		Fig. 7A–C  Proliferating tricholemmal cystic carcinoma. This huge neoplasm is malignant by virtue of its silhouette and its cytopathologic attributes. It is a carcinoma because the neoplastic cells that compose it are cohesive, and it is tricholemmal in differentiation because the epithelium resembles so closely that of normal outer sheath at the isthmus.