The WHO defined an Ameloblastic Carcinoma (AC) secondary type (dedifferentiated) intraosseous as a malignant neoplasm that "arises in a preexisting benign ameloblastoma. Dedifferentiated ameloblastoma is applied when morphologic features of typical ameloblastoma were noted. Microscopically, clusters or nests and islands of epithelium within a collagenous stroma are composed of a peripheral layer of polarized cells enclosing stellate to basaloid cells in the early transition of the de-differentiation stage. These cellular structures may show pleomorphism, frequent mitotic figures, indistinct cell membranes, focal necrosis, loss of cellular cohesion and infiltration along nerve bundles" [1]. According to the WHO, Unicystic Ameloblastoma (UA) represents an ameloblastoma variant, presenting as a cyst [1]. Cases associated with an unerupted tooth show a mean age of 16 years as opposed to 35 years in the absence of an unerupted tooth [2]. The mean age is significantly lower than that for solid ameloblastoma and there is no gender predilection [3], 5 to 15% of all ameloblastomas are of the unicystic type [4], but a Latin-American study showed that the unicystic type reached 60% [5]. Malignant transformation of UA is a very unusual phenomenon, and to date, only two cases of AC associated to an UA are published [6,7]. Zonula adherens and Tight Junctions (TJs) are membranal structures for cell-cell adhesion in epithelial and endothelial cells. These structures have barrier and/or fence functions and are composed by sets of proteins regulating the transfer of ions, water, and some macromolecules (barrier function). Proteins involved in fence function maintain cell polarity, recruit signaling proteins, and control the lateral diffusion of proteins within the lipid bilayer. Additional functions of TJ proteins are regulation of cell differentiation and proliferation. TJ proteins are composed of three major integral membrane proteins: claudins, occludin, and Junctional Adhesion Molecules (JAM proteins) [8-10]. Claudins are an important group composed of 27 proteins regarded as the backbone of the TJ, they maintain cell polarity, regulating the paracellular membrane selectivity and permeability [9]. Altered expression of claudins has been related to tumorigenesis, loss of polarity, cell motility, down regulation of cell-cell adhesion, and reorganization of the cytoskeleton. These processes are associated with lack of differentiation, neoplastic progression, cell invasion, survival, aggressiveness, recurrence, and regional and distant metastases [10,11]. To date, only two studies on claudin immunoprofile in odontogenic cysts and tumors are reported [12,13]. This report describes an unusual case of an UA associated with an AC and presents the results on the immune expression of claudins 1,3 and 9, and to assess its PCNA index.
