Co-existence of mixed meibomian gland and ductal adenoma with an apocrine sweat gland cyst in a dog: histological and immunohistochemical analyses.

A 14-year- old female Shih Tzu was presented with conjunctivitis, keratitis, an enlarged mass located on the left lower eyelid and a large subcutaneous cyst in the temporal region. The hematological and biochemical analyses revealed no significant issues. The mass and the cyst were taken from the base with 1.50 cm of the underlying tissue. On histological examination, the mass was made up of adenoid arrangements of sebocytes and basaloid reserve cells with low to moderate mitotic activity of basaloid cells. In addition, a large number of meibomian ducts with marked infiltration of mononuclear inflammatory cells and melanin pigment were observed in the ductal part of the tumor. The cyst was lined by a simple cuboid-like epithelium with no eosinophilic cuticular lining. Immuno-histochemical staining of the mass with CK14 showed positive reaction in the neoplastic basaloid reserve cells and adipocytes; but, not with CK18 and vimentin. Unlike, the luminal cells of the cyst were stained with CK18. The co-existence of mixed meibomian gland and ductal adenoma with an apocrine sweat gland cyst was diagnosed based on the clinical, histological and immunohistochemical findings.