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The WHO Histological Classification of Lung Tumours, published in 1967, has been revised. The main features are as follows: Squamous cell carcinoma (epidermoid carcinoma) has the same definition as in the original version, i.e., the identification of keratin and/or intercellular bridges by light microscopy. Three degrees of histological differentiation are described. Dysplasia and carcinoma in situ are discussed. Small cell carcinoma is divided into oat-cell carcinoma, an intermediate cell type and a category for oat-cell carcinomas combined with other major types. Adenocarcinoma includes the acinar, papillary and bronchiolo-alveolar forms and the solid carcinomas with mucus formation (previously part of the large cell carcinoma group). Mesothelial tumours are divided into fibrous, epithelial and biphasic subtypes. A number of less common tumours and tumour-like lesions are defined.

The clinical and histological features of 13 examples of pseudosarcoma of the skin are described. Found almost exclusively on the face, ear or nose of elderly persons, this lesion has standard microscopic criteria of malignancy in the way of abundant mitotic activity and/or cellular pleomorphism yet behaves apparently in a benign fashion. Conservative surgical excision is almost always curative.