Tetrathyridiosis and tubulopapillary carcinoma occurring simultaneously in the mammary gland of a cat.

This report describes a case of tubulopapillary carcinoma and concomitant tetrathyridiosis in a 5-year-old female cross-breed cat. A mass was located at right inguinal mammary gland and measured 5.5 × 5 × 3 cm in size with multilobulated to solid appearance. The cut surface of the mass had a centrally located large cyst (approximately 3 cm in diameter) surrounded by other smaller cysts. Histologically, the mass was diagnosed as tubulopapillary mammary carcinoma, intensely positive for AE1/AE3 cytokeratins. The cyst found at post-mortem examination was tetrathyridia of Mesocestoides species surrounded by inflammatory cells and a loose fibrous capsule. To the authors' best knowledge, this is the first description of a tubulopapillary carcinoma and tetrathyridiosis found simultaneously in the mammary gland of a cat.