Recurrent Adamantinoma With Fibrous Dysplasia-like Feature.

Adamantinoma (AD) is a rare, slow-growing primary malignant bone tumor characterized by a biphasic morphology of clusters of epithelial cells and spindle cell osteofibrous components. A strong relationship between AD and osteofibrous dysplasia (OFD) has been proposed, while fibrous dysplasia (FD) has been rarely associated with AD. We present an AD case that was followed and histologically evaluated 3 times over 6 years with different morphological patterns. The tumor in the primary biopsy and after complete resection showed classical features of AD and osteofibrous-like pattern, while the recurrent lesion presented with exclusively spindle cell morphology and was thus diagnosed as FD. However, the extensive immunohistochemical analysis in all 3 lesions revealed strong reactivity for pancytokeratin, vimentin, p63, and podoplanin, which are characteristic for AD. Although, in the FD-like section of the tumor from the first recurrence the positivity of podoplanin was stronger than pancitokeratin, which was variably positive on spindle cells. The present case highlights the problem of diagnosing AD based on a single biopsy with one tumor's component predominating over the other, and at the same time emphasizes the importance of using immunohistochemical staining for keratin and podoplanin when the histopathological features of (osteo)fibrous lesion can be linked to AD.