p73 and p63 are recently cloned genes that share considerable structural and functional homologies with the p53 tumor suppressor gene. These genes, unlike p53, express multiple mRNA isoforms with variable biologic functions, and their suppressor nature has yet to be confirmed. To determine the interrelationship between these genes in the tumorigenesis of head and neck squamous carcinoma (HNSC), we performed immunohistochemical analyses of their protein products and compared the data with clinicopathologic parameters in 38 patients. In histologically normal epithelium, p53 and p73 showed similar basal and/or parabasal expression, but that of p53 was weaker and discontinuous. p63 staining was noted in more suprabasal cellular layers and was stronger. In dysplasias, all three markers manifested variable but gradual increase in extent and intensity of cellular expression with histologic progression. In carcinomas, p63 was the most frequently expressed (94.7%), followed by p73 (68.4%) and p53 (52.6%). Significant statistical correlation was noted only between p63 and p73 expressions (P =.04). Although no statistical correlation was found between p53 and p63 or p73, p53-negative tumors overexpressed either p63 or p73. p73 expression was associated with distant metastasis and perineural/vascular invasion. Our study indicates that (1) p63 and p73 expression may represent an early event in HNSC tumorigenesis, (2) the lack of correlation between p73 or p63 and p53 expression suggests an independent and/or compensatory functional role, (3) p73 expression may play a part in HNSC progression, and (4) p73 and p63 may function as oncogenes in the development of these tumors.
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