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.

The expression pattern of two Ca2+‐dependent cell‐cell adhesion molecules, E‐and P‐cadherin (CD), in 25 primary gingival squamous cell carcinomas (SCC) was examined immunohistochemically. The occurrence of reduced‐type expression of both E‐and P‐CD increased significantly with the grade of carcinoma differentiation, culminating in a complete loss of P‐CD in poorly differentiated SCC. The occurrence of reduced‐type P‐CD expression also increased significantly with the mode of invasion, as was the case with E‐CD. Furthermore, no P‐CD molecules were detected in one of the six SCC having a diffuse, cord‐like invasion and in three of the six having a diffuse type of invasion. These findings suggest that the down‐regulation of these cell adhesion molecules closely correlates with the differentiation grade and mode of invasion of gingival SCC.

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