Correlation of histological subtypes, grading and lymphovascular invasion in canine mammary carcinomas

Histological diversity of canine mammary tumours (CMTs) provides little prognostic information. Hence, use of a histological grading system may be helpful for prognosis of CMTs. A total 59 canine mammary carcinomas (CMCs) were graded histologically. The carcinomas were classified as grade I, II, or III based on evaluation of the formation of tubular structures, nuclear pleomor- phism, and mitotic indices. Microscopic evidence of lymphatic invasion was also examined. Histologically, 26 (26/59; 44.07 %), 23 (38.98%), and 10 (16.95%) CMCs were graded in grade I, II and III respectively. Majority of solid carcinomas, anaplastic carcinomas, comedocarcinoma and squamous cell carcinoma were in histological malignancy Grade III, whereas most tubulopapillary carcinomas, complex carcinomas, carcinoma and malignant myoepithelioma, mixed carcinomas and malignant myoepithelioma were in histological malignancy Grade I. Variable numbers of tubular carcinomas, tubulopapillary carcinomas, solid carcinomas, carcinoma and malignant myoepithelioma, mixed carcinomas and malignant myoepithelioma shown intermediate malignancy Grade II. Lymphovascular invasion was detected in 10 (16.95%) CMCs cases. Of this 10 cases 2 CMCs were in grade I while 4 CMCs were in each grade II and grade III. Tubular carcinoma, micropaillary carcinoma, solid carcinomas, anaplastic carcinoma, carcinoma and malignant myoepithelioma and mixed carcinomas showed lymphovascular invasion. In conclusion, this study validated the Pena method of histopathological grading of CMCs. This grading system of CMCs could be used for future prognostic studies.