Histological grading and prognosis in dogs with mammary carcinomas: application of a human grading method

The human "Elston and Ellis grading method" was used in dogs with mammary carcinoma to examine its relation to prognosis in this species, based on a 2-year follow-up period. Of the 85 cases examined, 27(31.8%) had well-differentiated (grade I), 28 (32.9%) had moderately differentiated (grade II) and 30 (35.3%) had poorly differentiated (grade III) carcinomas. Two years after mastectomy, significant differences in survival between cases with different tumour grade were found; thus, survival was worse in dogs with grade III carcinomas than in those with grade II (P<0.05) or grade I (P<0.001) tumours. However, in dogs with simple carcinomas which had a less favourable prognosis than that of other carcinomas (P<0.001), there was no significant difference in survival between grade II and grade III cases (P=0.878), both having a very poor prognosis. Undifferentiated (grade III) carcinoma cases had a 21-fold increased risk of death as compared with differentiated (grade I and II) carcinoma cases. An increased risk (about 10-fold) was also associated with undifferentiated simple carcinomas as compared with differentiated ones. The predictive value of histological grade was not influenced by tumour size or age of the dog at mastectomy; nodal metastasis, however, worsened the prognosis (P<0.001). Routine use of this human grading method would help the clinician to make a more accurate prognosis in the interests of post-surgical management in dogs with mammary carcinomas.