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We describe 11 poroid neoplasms with sebaceous differentiation, including a metaplastic (sarcomatoid) carcinoma arising in association with an apocrine poroma. Six lesions had the silhouette of a classical poroma, 3 of poroid hidradenoma and 1 of dermal duct tumor. In all cases, sebaceous differentiation was identified as clustered or solitary, mature sebocytes occurring mainly at the periphery of intradermal cellular aggregations, accompanied by sebaceous ducts. In one poroma, clusters of sebocytes were seen within intradermal aggregates and intraepidermally. In 1 of the 3 poroid hidradenomas, the eosinophilic cuticle lining the cyst was crenulated in foci associated with sebocytes. In none of the cases were there signs of follicular differentiation. One poroma, in addition to sebaceous differentiation, showed decapitation secretion in some ductular structures. The single carcinoma was an ulcerated oval to spindle cell neoplasm surrounded laterally by the residuum of a poroma containing groups of sebocytes. The epithelial islands of the poroma were prominently keratinized and blended gradually with the pleomorphic cells of the metaplastic carcinoma that immunohistochemically stained focally for cytokeratins and simultaneously showed strong vimentin expression. Our study supports previous findings that sebaceous differentiation can be identified not only in classical poroma but also in the related lesions known as dermal duct tumor and poroid hidradenoma. Occurrence of metaplastic carcinoma in association with apocrine poroma is a rare event which indicates the existence of a malignant counterpart of the latter entity, which can be descriptively referred to as "sarcomatoid apocrine porocarcinoma."

Syringocystadenoma papilliferum is a benign tumor most commonly located on the scalp or face, and it often arises within a nevus sebaceus of Jadassohn. We describe a 61-year-old man with syringocystadenoma papilliferum developing within a nevus sebaceus with sebaceous differentiation in an intradermal tubular apocrine component of the syringocystadenoma papilliferum. Although some adnexal neoplasms that develop in association with a nevus sebaceus may exhibit conjoint sebaceous, follicular, or apocrine differentiation, reflecting close embryological relations of the folliculosebaceous-apocrine unit, the feature we report on has not previously been described to the best of our knowledge.

Skin adnexal type tumors situated in the parenchyma of the breast are very rare. We report herein a case of solid-cystic hidradenoma of the breast. The tumor was situated in the parenchyma of the breast of a 55-year-old female and showed no connection to the overlying skin on ultrasound and radiology investigations, grossly and microscopically. Histologically, the tumor was identical to its cutaneous counterpart and was surrounded by breast tissue. The neoplasm was composed of solid and cystic areas. The cystic component, which predominated in the lesion, was filled with homogeneous eosinophilic material. The solid component consisted of several nodules with vague lobulated architecture protruding into the cystic spaces. The nodules were composed of cuboidal monomorphous cells that were continuous with larger polygonal cells and rare, large mucinous cells with basophilic granular cytoplasm. Several mammary ducts in close proximity to the tumor showed features of columnar cell hyperplasia. A 120-bp METC1/MAML2 fusion transcript was identified by RT-PCR and subsequent sequencing technique. This t(11;19) translocation has been reported in approximately 50% of hidradenomas of the skin.

Tubular adenoma (TA) and syringocystadenoma papilliferum (SCAP) may show histopathological overlap, with some lesions having features of both neoplasms (SCAP + TA). TA has been recently suggested to represent a carcinoma. Four observers blindly assessed 67 cases of TA, SCAP, and their lookalikes (poroma, apocrine adenoma, apocrine carcinoma; all lesions focally featuring a pseudopapillary pattern), and classified the lesions into one of four categories: (1) TA, (2) SCAP, (3) SCAP + TA, and (4) others. Lesions were also classified as benign or malignant. In only 29 cases was there unanimous agreement among the four observers, who classified 22 lesions as TA, three as SCAP, and four cases as others. Of the 38 cases where there was interobserver diagnostic variation, in 30, the diagnosis varied between TA or SCAP or SCAP + TA; the remainder fell in the others category. Analysis of the factors leading to interobserver variability indicated that diagnostic problems occurred when there were any of the following: epidermal acanthosis, papillomatosis, connection of the neoplastic tubules to the overlying epidermis and/or follicular infundibula, and plasma cell infiltration. These features accounted for the morphological overlap between TA and SCAP. All observers agreed that the lesions were benign; the only apocrine carcinoma included was recognized as such by all observers. From the study, it was concluded that TA may arise in the deep dermis without any epidermal connection, or, in other cases, it may be more superficially located with or without an epidermal connection. It may be reasonably inferred that, possibly as a response to infection, there may be accompanying plasma cells and variable acanthosis and papillomatosis, such that the appearances are those of "pure" SCAP, or lesions may have features "intermediate" or overlapping between TA and SCAP.

Twelve cases of spiradenocylindromas, which revealed features of both spiradenoma and cylindroma in the same tumor mass, are presented. Nine female patients had multiple neoplasms occurring mostly on the scalp, and two female and one male patient had a solitary cutaneous lesion. Three of the female patients with multiple cutaneous tumors had a familial history of similar cutaneous neoplasms. In one of the patient's family, the multiple cutaneous tumors were known to occur in multiple family members in four consecutive generations. One patient with multiple cutaneous lesions was known to have associated multiple kidney cysts as confirmed by computed tomography. Histologically, spiradenocylindromas are composed of intermixed areas that are either of typical spiradenoma in appearance or of typical cylindroma appearance. Apocrine and trichoepitheliomatous differentiation seen in two cases in the present series points to spiradenomas, as well as cylindromas, having complex hair follicle (folliculo-sebaceous apocrine) rather than eccrine differentiation. The presence of lymphoid tissue was a histological feature in the present series, which was prominent in all the spiradenomatous parts of the tumors and which was scanty or practically absent in all the cylindromatous parts. The selective presence of lymphocytes in spiradenoma and an absence in cylindroma suggest that spiradenomas have the unique property of attracting lymphocytes. The malignant tumors arising in three patients in the present series had the morphology of a poorly differentiated epithelioid neoplasm. Three patients died of the disease and the other patients were either free of disease or alive with disease 1-30 years on follow up.