In adamantinoma of long bones, an osteofibrous dysplasia-like form with scattered epithelial elements and a classic form with abundant epithelium are distinguished. Osteofibrous dysplasia-like adamantinomas occur in children and adolescents and behave relatively benign, whereas classic adamantinomas predominate in adults and have a more aggressive clinical course. Because some osteofibrous dysplasia-like tumors have progressed to classic adamantinomas, it is hypothesized that the former is a potential precursor of the latter, showing mesenchymal-to-epithelial transformation. We report a new morphologic variant of adamantinoma in three patients with sarcomatoid transformation of the epithelial component: one in a primary tumor and two in local recurrences. One patient died of metastatic disease. Histologically, the tumors showed loss of the original characteristic epithelial differentiation with transition to fields of highly pleomorphic cells without epithelial features, high mitotic count, and deposition of osteoid and chondroid matrix. These dedifferentiated areas showed pankeratin positivity as well, although there were some changes in keratin subclass profile compared with other classic adamantinomas. This peculiar variant of long bone adamantinoma shows that in addition to mesenchymal-to-epithelial transformation in the early stage of development, progression to an aggressive subtype may be associated with epithelial-to-mesenchymal transition ("sarcomatoid dedifferentiation"), in which the epithelial immunophenotype is conserved. Thereby it may serve as an example of the plasticity of the mesenchymal phenotype. When confronted with a biopsy of a cortical tumor of the tibia showing sarcomatoid morphology and keratin positivity, adamantinoma should be included in the differential diagnosis, as its distinction has important implications for treatment and prognosis.

Adenomyoepithelioma is a rare breast tumor. Histologically it may disclose different patterns of growth, and some additional features may result in diagnostic errors. We describe 2 cases of adenomyoepithelioma of the breast initially examined by fine-needle aspiration biopsy (FNAB). Cytologic features included hypercellularity, clusters of epithelial and myoepithelial cells with occasional intranuclear inclusions, prominent apocrine metaplasia, and foam cells. Histologically, both tumors were diagnosed as adenomyoepithelioma tubular-variant, with prominent myoepithelial clear cells, apocrine metaplasia, and foci of squamous metaplasia. Immunohistochemically, the tumors showed strong positivity for keratins CAM 5.2, AE1/AE3, and EMA in the epithelial component, while the myoepithelial cells reacted with muscle-specific actin (A14 and HHF35) and S-100 protein. We point out that FNAB in this rare tumor may exhibit a varied spectrum of cells that may result in confusion with other lesions, and we call attention to the presence of intranuclear inclusions. The latter observation in the present cases by cytologic and histologic assessment provides an additional feature to the morphological characteristics of adenomyoepithelioma of the breast.

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A parotid gland mass in an elderly man was diagnosed as an oncocytic neoplasm with cellular pleomorphism and cytologic atypia by fine-needle aspiration. The histologic features showed a primary parotid malignant oncocytoma with metastasis in regional lymph nodes.

Thyroid adenomas containing adipose tissue are rare. Only scattered case reports have been recorded. We describe an additional case of an adenolipoma of the thyroid gland, incidentally found in residual gland subsequent to excision of a papillary carcinoma.