Unexpected Cytological Detection of <i>Leishmania infantum</i> within the Secretion of a Canine Mammary Carcinoma

Mammary tumors are one of the most common neoplasms in female dogs, and cytology represents a non-invasive diagnostic method. The protozoal pathogen <i>Leishmania</i> spp. was previously demonstrated in canine mammary glands. An eight-year-old, female-spayed Doberman was imported from Crete, Greece, three years before the first presentation. The dog was presented due to a mammary tumor two years after adoption. The clinical examination revealed fever and weight loss. Smears of the mammary secretion were investigated cytologically. Multiple atypical epithelial cells with moderate to marked criteria of malignancy were detected. Furthermore, amastigotes were visible intra- and extracellularly. The diagnosis of <i>L. infantum</i> infection was based on a positive PCR out of the cytological smear, and a positive serology. Mammary carcinoma and granulomatous inflammation with amastigotes were confirmed by histopathology. We aimed to provide a complete report of cytological, histopathological, hematological, and biochemistry findings in a dog with <i>L. infantum</i> in the mammary glands with focus on trans-mammary pathogen transmission as a potential alternative way of spreading <i>Leishmania</i> infections. Canine leishmaniasis should be a potential differential diagnosis in dogs with lesions and/or inflammation in the mammary glands and a history of presence in areas endemic for <i>L. infantum</i>, especially the Mediterranean in Europe.