Benign and malignant mixed tumours of the lung.

Ten patients are presented with tumours complying with the criteria established by the World Health Organization for mixed tumours of the lung'. A slowly growing intrabronchial neoplasm indistinguishable from a pleomorphic adenoma (mixed salivary tumour) and a peripheral circumscribed tumour with most of the features of a chondromatous hamartoma were considered benign. Of eight malignant neoplasms two were regarded as pulmonary blastomas', one with a benign epithelial tubular component and the other with cytological evidence of malignancy in the tubular epithelium; in both, the stroma was embryonic' and pleomorphic. Three tumours were considered carcinosarcomas with a mainly epidermoid epithelial component and a pleomorphic spindle-cell connective tissue component. In the remaining three tumours the malignant epithelial component showed mixed, viz., epidermoid, tubular, and a variety of undifferentiated appearances, while the stroma' exhibited features seen in both blastomas and carcinosarcomas. These three neoplasms were considered transitional'. The spectrum of appearances encountered constitutes, in our opinion, a serious objection to the thesis that peripheral pulmonary blastomas and carcinosarcomas are distinct entities with a separate histogenesis. Exceptions were found to blastomas' being peripheral and carcinosarcomas being central growths. A case is made for reclassification of the benign and malignant neoplasms included in the WHO group IX `mixed tumours of the lung'.