Alveolar trapping in pulmonary carcinomas.

Sixty surgically resected pulmonary carcinomas have been studied by light and electron microscopy for engulfed alveolar cavities within the tumour mass. Alveoli had been incorporated in twelve cases, ten epidermoid (squamous) carcinomas and two adenocarcinomas. They were lined by granular pneumocytes and cells transitional between granular and membranous pneumocytes. The lining cells showed a positive reaction to alkaline phosphatase. Cellular debris, leucocytes and mucus could be seen within the residual lumen. It is concluded that alveoli commonly found within pulmonary carcinomas. Accurate histological classification requires these to be differentiated from true neoplastic spaces.