Histopathological study of rat mammary adenocarcinoma after protein A administration

Protein A was purified from Staphylococcus aureus Cowan I and administered subcutaneously for a period of six weeks to a 7,12-dimethylbenz(alpha)anthracene-induced rat mammary adenocarcinoma model, which resulted in a significant reduction in tumor volume. Considerable fibrosis, inflammatory reactions, cellular debris, and edema were the hallmarks of tumor necrosis caused by administration of protein A. Calcification, which may be the replacement of earlier necrosis, also was observed. Thick eosinophilic secretions were observed in the lumina of the breast tubules. The results suggest that inflammatory mechanisms may be activated, accounting for the tumoricidal effects observed following treatment with protein A.