The molecular characterization of mammary tumours represents a new stage in the development of effective predictive models and targeted therapies. The aim of this study was to evaluate the relationship between the molecular phenotype of a primary feline mammary tumour and that of a related lymph node metastasis. Twenty-one mammary tumour samples and their lymph node metastases were selected and evaluated immunohistochemically for expression of oestrogen receptor, progesterone receptor, human epidermal growth factor receptor 2 (c-erbB-2), cytokeratin 5/6, cytokeratin 14, cytokeratin 19 and protein 63. Mammary tumours were classified into five subtypes: luminal A, luminal B, c-erbB-2 overexpressing, basal-like and normal-like, based on an algorithm applied in both human and veterinary medicine. Concordance between the primary tumour and its lymph node metastasis was detected in 12 of 21 cases (57.1%). In the remaining nine cases (42.9%) there was discordance in the molecular profile at the two sites. Therefore, the tumour molecular profile must be evaluated in both sites in order to obtain definitive identification of the tumour profile (or profiles) and to plan an appropriate therapy.
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