Bleomycin lung damage: the pathology and nature of the lesion.

The pathology of two cases of pulmonary damage due to bleomycin is described. The drug damages the alveolar walls. A sequence of pathological changes could be traced commencing with oedema, intra-alveolar fibrin and haemorrhage, followed by type II pneumocyte hyperplasia associated with bronchial epithelial squamous metaplasia. This led to intra-alveolar and alveolar wall collagen formation producing diffuse interstitial fibrosis with microcyst formation associated with cuboidalization of the epithelium. These changes are similar to those seen in experimental bleomycin damage in mice, where it has been shown that the changes are the result of vascular damage and type I pneumocyte necrosis. It is inferred that human diffuse alveolar damage develops in the same way.