Primary tumours are rare, but cases of osteoma and of lipoma have been recorded.

Primary cancer occurs in the pleura, forming, according to some, Endothelial cancer. In most of the recorded cases there has been great thickening of the pleura and the tumour formation was in some apparently related to the lymphatics. The pleura has usually contained a bloody fluid and has been coated with coagulum sometimes with the appearance of acute pleurisy. In some cases there has been metastasis to other organs.

In a case observed by the author there were numerous tumours on the pleura, and also, by coalescence, larger masses, forming a layer of considerable thickness. The tumours were almost continuous over the pleura, and there was no tumour anywhere else! The sac was greatly distended with a blood-coloured fluid, measuring 140 ounces, which had deposited a loose brown coagulum. During life the case resembled one of acute pleurisy with great effusion. Paracentesis was twice performed, and a bloody fluid withdrawn.

Microscopic examination showed the tumour to be a superficial cancer of the pleura. There was the usual stroma enclosing epithelial cells, which were frequently fatty. The tumours were not at all deep in the substance of the pleura, there being always a layer of connective tissue beneath them. (See Glasg. Med.. Jour., July, 1889).