Classification of Feline Mammary Tumours: Prognostic Morphology and Markers Expression

Most feline mammary tumours are aggressive carcinomas (80-90%) with poor prognosis. When compared to canine tumors, they are less heterogeneous, with few complex and mixed tumours. A new histologic classification of canine mammary tumours was recently published. Our study analyzes the morphology of feline mammary neoplasms and compares them with their canine counterparts. We evaluated phenotypic and prognostic markers (pancytokeratin – panCK, CK8_18, CK5, CK14, calponin, alpha smooth muscle actin, vimentin, p63, beta-catenin, E-cadherin, estrogen and progesterone receptors, Ki-67, HER-2, p53), which were compared with morphologic subtypes, postsurgical survival and normal/hyperplastic glands. In normal feline mammary glands, undifferentiated basal/myoepithelial cells (CK5þ, CK14þ, p63þ, vimentinþ) were confined to proximal ducts; vimentin expression was luminal and ductal, with pronounced coexpression with CK14 exclusively in terminal intralobular ductules. In interductal lobules, luminal cells were negative for both these markers. We identified several less aggressive morphological subtypes of mammary tumors, including ductal adenomas/carcinomas and intraductal papillary adenomas/carcinomas that exhibit specific immunomarker expression (vimentin- and CK14þ basal/myoepithelial cells), with prolonged patient post-surgical survival. Mammary non-ductal neoplasms expressed vimentin (95% of tumours, 10-90% positive cells). There was a significant correlation between vimentin and CK14 (90% of tumours, 6-100% positive cells) expression, which was inversely related to the expression of estrogen and progesterone receptors, CK8_18 and improved prognosis. This suggests a possible role of vimentinþ/CK14þ cell population of the terminal end intralobular ductular structures in aggressive feline neoplasms. Thus the newly proposed canine mammary tumour classification may be applicable to feline mammary tumors, with a significant role for specific immunomarkers in determining prognosis.