Mammary tumours are second most common tumour in dogs which accounts 50 per cent of all neoplasms. Due to its close similarities in structure and biological behavior, the work report and animal species could be used as a model for human breast cancer study. The commonly used prognostic survival analyses by clinical and biological behavior are not convincing much the clinician, dog owners and veterinary oncologists. Hence, there is a need to use an alternate approach using different molecular immunohistochemical protein analysis, mutational study, etc., which have been recently used for assessing the survivability. This book is originally designed from Ph.D., thesis submitted to the Tamil Nadu Veterinary and Animal Sciences University, Chennai, India which explores the use of different histochemical markers viz., p53 protein over expression (mutant p53 gene and protein expression), PCNA and Caspase-3 reactivity, it also explores the lipid peroxidation and anti-oxidant profiles which in turn useful for accurate prognosis and also to establish the appropriate treatment.