Unusual finding in a nipple discharge of a female dog: dirofilariasis of the breast.

We report a case of dirofilariasis of the breast occurring in a 6-yr-old Bernese female dog living in central Italy presenting with a breast lump, diagnosed on cytological examination of nipple secretion fluid smears. The direct smears of nipple discharge revealed clusters of glandular cells characterized by mild pleomorphic appearance and the presence of some nematodes of about 350 microm in length in the background. The smears also contained several inflammatory cells, including eosinophils. Both the Knott and the antigen tests were negative for Dirofilaria immitis. The morphological features of this round worm is compatible with that of Dirofilaria repens. The case describes an unusual finding of dirofilariasis presenting as a breast lump, simulating an inflammatory breast carcinoma.