A review of the clinical, radiologic, and histologic features of 25 cases of long bone
adamantinoma is presented. To answer some questions concerning the nature of these
tumors, relevant tissue markers were analyzed in seven cases using immunohistochemical assays. This study confirmed the epithelial nature of long bone
adamantinomas irrespective of their wide-ranging morphologic patterns that can mimic
tumors of various origin. On the basis of distinct radiologic, histologic, and immunohistochemical patterns, a new type of
adamantinoma termed "differentiated
adamantinoma" could be distinguished from the classic long bone
adamantinomas. The diagnostic features characteristic of the differentiated
adamantinoma include: patient age (first two decades), intracortical location of the entire lesion, uniform predominance of an
osteofibrous dysplasia-like pattern, and scattered positivity of epithelial elements for
cytokeratin. We postulate that the predominance of an
osteofibrous dysplasia-like pattern in differentiated
adamantinoma is the result of a secondary reparative process overgrowing matured and regressing
tumor tissue. It is possible that this process may lead to the total elimination of recognizable
tumor cells from the lesion. Therefore,
osteofibrous dysplasia (
ossifying fibroma) of long bones, which has a similar anatomic location, age distribution, and radiologic appearance as differentiated
adamantinoma, may, in some cases, represent the evolution of an underlying
adamantinoma. Our analysis suggests that long bone
adamantinoma could be another member of the unique family of
tumors that may regress spontaneously.