Validation of tissue microarray for molecular profiling of canine and feline mammary tumours

Tissue microarray (TMA) is a high-throughput method adopted for simultaneous molecular profiling of tissue samples from large patient cohorts. The aim of this study was to validate the TMA method for the molecular classification of canine and feline mammary tumours. Twelve samples, five feline and five canine mammary tumours and two canine haemangiosarcomas, were collected. TMA construction was based on Kononen's method of extracting a cylindrical core of paraffin wax-embedded 'donor' tissue and inserting it into a 'recipient' wax block. Seven consecutive sections from each tissue array block were subjected to immunohistochemistry (IHC) using primary antibodies specific for oestrogen receptor (OR), progesterone receptor (PR), c-erbB-2, cytokeratin (CK) 5/6, CK14, CK19 and p63. The same panel of antibodies was applied to the full sections from all cases. Comparison between full sections and TMA scores revealed different results depending on the antibodies. Labelling for OR, PR, CK19 and p63 showed total concordance, c-erbB2 (score +2, +3) was concordant in nine out of ten cases, CK5/6 and CK14 in eight out of ten cases. The TMA platform preserves the molecular profile of canine and feline mammary tumour markers, representing a useful tool for rapid and cost-effective analysis for the first phenotypic screening using OR, PR and c-erbB2 antibodies. Basal cytokeratin, used for triple negative identification, shows a multifocal 'niche' expression pattern, for which IHC of the full section or multiple core array is recommended.