Trichoepithelioma and Spiradenoma Collision Tumor
The coexistence of more than one cutaneous adnexal neoplasm in a single biopsy specimen is unusual and is most frequently recognized in the context of a nevus sebaceous or Brooke-Spiegler syndrome, an autosomal-dominant inherited disease characterized by cutaneous adnexal neoplasms, most commonly cylindromas and trichoepitheliomas. The differential diagnosis includes adenoid cystic carcinoma arising within a spiradenoma, cylindroma and spiradenoma collision tumor, microcystic change within a spiradenoma, mucinous carcinoma arising within a spiradenoma, and trichoepithelioma and spiradenoma collision tumor.
Cylindromas are composed of basaloid islands interconnected in a jigsaw puzzle configuration (Figure 5B).4 Similar to spiradenomas, they also are composed of 2 cell populations. Characteristically, the tumor islands are outlined by a hyalinized eosinophilic basement membrane. Hyalinized droplets of basement membrane zone material also may be noted in the islands. Unlike spiradenomas, they lack both intratumoral lymphocytes and a trabecular growth pattern. Although spiradenocylindromas (cylindroma and spiradenoma collision tumors) are perhaps the most common collision tumor associated with Brooke-Spiegler syndrome, there is no evidence suggesting the presence of a cylindroma in the current case.
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Primary cutaneous mucinous carcinoma is a rare neoplasm with a predilection for the eyelids; lesions occurring outside of this facial distribution, particularly of the breast, warrant a workup for metastatic disease.7 It typically occurs in the deeper dermis with involvement of the subcutaneous fat and is characterized by delicate fibrous septa enveloping large lakes of mucin, which contain islands of tumor cells (Figure 6). It has not been reported in association with spiradenomas. In addition, the tumor cells typically are CK7 positive.
