Based on the promising results of this pilot study the aim of the present retrospective study was to investigate serum Ki-67 in larger groups of dogs with malignant tumours, to detect differences in regard to tumour entity, whether there is a correlation between Ki-67 and certain inflammatory cells measured in the blood and whether serum Ki-67 could be a potential pan tumour marker for future screening tests for canine malignancies. The gene discussed is MKI67; the disease is cancer.