Observations on the correlation between histological grading and survival times of canine and feline malignant mammary tumours

The histological grading used in the prognosis of mammary cancer in animals has usually concerned the dog, mainly following the criteria by Gilbertson and coworkers in 1983 [1] and by Lagadic and Estrada in 1990 [2]. The former method (Method 1), simplified and extended to the cat by Mandelli and co-workers in 1987 [3], is based on the evaluation of nuclear grade, duct grade and staging, each one considered separately to get prognostic information. The latter (Method 2) considers nuclear pleomorphism, tubular differentiation and number of mitosis together to obtain a single final value. In the present study, 27 canine and 16 feline mammary malignancies were diagnosed following the WHO classification (1974) and graded according to Methods 1 and 2. None of the animals had evidence of metastases at the time of surgical excision of the tumour. Chest radiographs and abdominal echographs were taken every two months for a two-year period. Two follow up parameters were evaluated: the survival time (ST) and the cancer-free interval (CFI). Method 1: staging revealed as most predictive for both species: animals bearing non-infiltrating tumours had a better prognosis than those with infiltrating neoplasms (P0.05) in both dogs and cats. Method 2 did not produce predictive results in the dog (P