Definitions of basal-like
breast cancer phenotype vary, and microarray-based expression profiling analysis remains the gold standard for the identification of these
tumors. Immunohistochemical identification of basal-like
carcinomas is hindered with a fact, that on microarray level not all of them express basal-type
cytokeratin 5/6, 14 and 17. We compared expression of
cytokeratin 5, 14 and 17 in 115 patients with operable
breast cancer estimated by real-time RT-PCR and immunohistochemistry. Despite the method of dichotomization and statistical analysis, there were cases with discordant results comparing immunohistochemistry and RT-PCR analysis. For dichotomisation based on quartiles and ROC, 14% of cases were negative on immunohistochemical examination for CK5/6, but presented high CK5
mRNA levels. There were also 48-55% cases, which were CK5/6-immunopositive, but were negative by
mRNA examination. Similar discordances were observed for CK14 and CK17. Basal
keratin mRNAs did not correlate with ER
mRNA levels, while immunohistochemistry produced significant relationship with ER status. Our observation suggest that both method may produce different results in a small proportion of cases. Discordance between immunohistochemistry and RT-PCR may confound attempts to establish a simple methods for identification of basal-like
tumors.