Two rare cutaneous neoplasms in horses: apocrine gland adenocarcinoma and carcinosarcoma

Two rare equine cutaneous neoplasms, an apocrine gland adenocarcinoma and a carcinosarcoma were diagnosed in a 17-year-old pony and a 14-year-old mare, respectively. The apocrine gland adenocarcinoma was present on the prepuce. Histologically, papillary projections of low cuboidal to columnar epithelial cells were generally well differentiated, and surrounded dilated acini. Stromal invasion was present, but vascular and lymphatic invasion was not seen. The carcinosarcoma was present in the right flank of the mare. Two discrete cell populations were characterized histologically. One portion of the mass was composed of elongated, loosely arranged mesenchymatous cells; the second population consisted of dense sheets of pleomorphic, basophilic cells forming irregular acini.