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Immunohistochemical analysis was performed to determine the localization of epidermal growth factor receptor (EGFR) in ameloblastomas. Ameloblastoma samples were classified into follicular, plexiform, and basal cell types. The number of cases in each category was 17, 19 and 3, respectively. Ameloblastomas, disregarding their histological type, consist of two cell forms: peripheral columnar cells and central stellate cells. The frequency of EGFR expression was much higher in the latter than in the former (P < 0.005). On analysis with respect to histological types, the frequency of EGFR expression in columnar cells was not significantly different between the follicular and the plexiform types, but was observed more frequently in the stellate cells in the follicular than in the plexiform ameloblastomas (P < 0.05). This pattern of EGFR expression was not consistent with the PCNA staining pattern, but was similar to that of keratin expression which we have reported previously. The present study suggests that EGFR expression in ameloblastomas is closely associated with tumour differentiation, and squamous differentiation in particular.

Immunohistochemical investigations were carried out on the localization and expression of the Ca2+‐dependent intercellular adhesion molecule E‐cadherin in human gingiva and gingival carcinoma. Although E‐cadherin did not appear in the parakeratinized layer of either clinically healthy or inflamed gingiva, it did appear strongly in the prickle layer and somewhat more weakly in the basal layer. Immunogold particles reactive to anti‐E‐cadherin monoclonal antibody in the electron microscopic findings were localized only in the vicinity of the desmosomes of the prickle and basal layers. In the case of gingival carcinoma, although E‐cadherin was strongly expressed in the cells surrounding the keratinized region in the cancer nests, the expression decreased towards the marginal portion of the cancer nests. The distribution of E‐cadherin in these cells may be dependent on the condition of the cancer cells that are potentially invasive. These findings suggest that cells of the parakeratinized layer of gingiva and cells of the marginal portion of the gingival carcinoma nests may easily detach or invade. In addition, the findings suggest that the gingival carcinoma used in this study tended to be invasive.