Localized amyloidosis in canine mammary tumors

Histopathologic and immunohistochemical examinations were performed on loca lized amyloidosis associated with mammary tumors in two dogs. These tumors were identified as adenoma and adenocarcinoma. An acellular, amorphous pale eosinophilic material (amyloid) was observed in the lumina of acini lined by neoplastic cells and in the stroma of the tumors. Concentrically laminat ed pale eosinophilic bodies (corpora amylacea) were also found in the lumin a of the acini. Amyloid and corpora amylacea stained positively with Congo red with and without 5% potassium permanganate pretreatment and revealed a green birefringence under polarized light. Corpora amylacea showed an occas ional Maltese-cross pattern. Immunohistochemically, amyloid and corpora amy lacea usually stained positively with anti-bovine alpha-casein antibody but negatively with anti-human amyloid AA, anti-bovine kappa-light and lambda- light chains, anti-human lactoferrin, anti-human transferrin, anti human se cretory component, and anti-human polyglucosan antibodies. These findings s uggested that the amyloid deposition in these canine mammary tumors was rel ated to lactating casein.