The pathology of oral cancer and precancer

Abstract

Oral cancer is the sixth most common cancer worldwide and represents about 5.5% of all malignancies. In the Western world it is less common, but the incidence is increasing and the mortality rate has not improved for decades. Although most oral cancers probably arise in clinically normal mucosa some are preceded by a precancerous lesion which indicates an increased risk of cancer development at a particular site. The histopathologist's role is to recognize pathological features which indicate high risk and to provide prognostic information from examination of excised tumours. The most common precancerous lesion is a white patch on the oral mucosa referred to as a leukoplakia. These show variable clinical features ranging from relatively innocuous flat white plaques to verruciform or red and white speckled lesions. A proportion of precancerous lesions show features of cytological atypia which are usually graded as mild, moderate or severe. The degree of epithelial dysplasia is a useful guide for the mangement of such lesions. 1 1 Most oral malignancies are squamous cell carcinomas which are usually well differentiated and show similar features to squamous cell carcinomas elsewhere. Although a number of grading systems are available, of most practical value in routine diagnosis is an evaluation of the depth and pattern of invasion which has been shown to correlate most closely with tumour behaviour. Lesions with a diffuse or reticular pattern of invasion with small cords or single cells infiltrating the connective tissues have the worst prognosis. This infiltrative pattern also correlates with local lymph-node metastasis and when examining a neck dissection the histopathologist must pay particular attention to the level of nodal involvement in the neck and to extracapsular spread from involved nodes. Particular diagnostic difficulties may arise when variants of squamous cell carcinoma are encountered. These include anaplastic lesions, spindle cell carcinoma, adenosqumous carcinomas and basaloid squamous cell carcinoma. Occasionally benign lesions may show pseudoepitheliomatous hyperplasia which may be mistaken for malignancy.