Mucus‐secreting ‘alveolar‐cell’ tumour of the lung: a histochemical comparison of tumours arising within and outside the lung

Five cases of mucus‐secreting ‘alveolar cell carcinoma’ are described, two of primary pulmonary origin and three metastatic from breast or pancreas. Mucin histochemistry demonstrated qualitative and quantitative differences between the mucopolysaccharides produced by these two groups of tumours. Hyaluronic acid production was restricted to the primary lung tumours. Greater quantities of acid sulphomucins were found in the two tumours arising in the lung and more neutral mucins in the three tumours metastatic from extra pulmonary primaries. It is proposed that mucus‐secreting alveolar cell carcinomas represent an unusual, and saprophytic relationship between the metastatic cells of well‐differentiated adenocarcinomas and the lung. As the malignancy of the tumour cells increases, so the ability to produce specific mucins decreases and, simultaneously, the tumours cease to maintain their alveolar pattern.