A primary lung cancer can produce a cavity in three ways. The first is 'cavitary necrosis' due to breakdown of the growth itself. The second is 'stenotic abscess' due to infection and breakdown of the lung parenchyma distal to bronchial obstruction caused by the growth. The third type is 'spill-over abscess'.In The single most important and noteworthy feature in the present series was that oat-cell carcinoma hardly ever undergoes necrosis. Out of a total of 95 cases observed, only three showed necrosis, and this was minimal and characteristically devoid of cavitation. In oat-cell carcinoma vascular invasion and tumour plugging was not observed, though all showed rapid growth and most of them blocked the lobar bronchi completely. In the light of the present study, the main factors responsible for tumour necrosis were found to be gradual bronchial obstruction and associated vascular involvement, though in many cases an inherent propensity of the tumour played a major role.A cavity or an abscess in the lung is defined as an abnormal hollow space within the lung parenchyma. Cavitation is one of the commonest phenomena in the lung. The

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Pulmonary blastomas are extremely rare subpleural tumours consisting of relatively welldifferentiated branched tubular glands which resemble fetal lung tissue embedded in a malignant mesodermal stroma. The previous 13 established cases reported up to June 1969 are now supplemented by a fourteenth. The patient was a 32-year-old man who developed acute pain in the right chest followed by a haemorrhagic pleural effusion. At thoracotomy a yellowishwhite necrotic and vascular tumour was located lying loosely in the fissure between the upper and the middle lobes. The histological appearance of the tumour was unusual in that the mesodermal element was very variable and in different areas simulated fibrosarcoma, leiomyosarcoma, lipomyxosarcoma, and malignant haemangiopericytoma. This diversity of mesodermal proliferation is best explained on the basis that the tumour has originated in an embryonic or pleuripotential type of mesenchyme, the site of which is probably in the periphery of the lung.