Similar differences were observed in an opposite direction – some cases which were positive by immunohistochemistry

were regarded as being negative by real-time RT-PCR. For CK5/6, there is a theoretical possibility that cells may express only CK6 and not CK5, but the same observation was made for CK14 and CK17. Possibly, the amount of immunopositive cancer cells in the sample was too small to give positive results by RT-PCR when mRNA levels were dichotomized. Moreover, for both types of discordances, it may be one universal explanation: because of the heteregeneity of the tumor, tissue examined by immunohistochemistry was not exactly the same tissue which was examined by real-time RT-PCR. We have found that basal keratin mRNA does not inversely correlate with Selleck GSI-IX ER mRNA level. This is an interesting observation, as in the published studies with the use of microarray technology such correlation is clear [1–3]. But when our samples were divided regarding basal keratin status on the basis of immunohistochemistry results, we observed significant relationship with ER status, estimated both by RT-PCR and by immunohistochemistry. It shows that immunohistochemistry may be a better method than RT-PCR in rendering a biological difference of basal-like tumors.

Studies that were conducted to establish which immunohistochemical markers BAY 80-6946 cost were helpful for the best definition of basal-like tumors gave different results [18–22]. Rakha

et al. suggested that only expression of basal-type cytokeratins (CK5/6 and CK14) should be included PRKACG in such definition [21]. In their study, no other marker was related with worse prognosis. More recently, some authors have claimed that EGFR expression should be added to the panel, and even in the absence of basal-cytokeratins, ER- and HER2-negative tumors presenting EGFR should be regarded as basal-type ones [5, 20, 21]. Nielsen at al. determined that 13 of 21 basal-type cancers from microarray study were CK5/6-positive by immunohistochemistry, 12 of them were EGFR-positive, and 6 of them were c-KIT-positive [5]. However, these authors regarded as a positive case even the weakest reaction. They also found that EGFR-positivity was correlated with basal-type gene expression and was related with worse survival; the same applied to CK5/6-positive tumors. This observation is encouraging but it is still questionable that EGFR-positive tumors should be named as “”basal-type”". Fulford et al. found a good correlation with clinical outcome when as the “”basal-like”" tumors were only regarded the cases with the presence of keratin 14 [22]. Summarizing, we have demonstrated a discordance between real-time RT-PCR and immunohistochemistry in assessing basal-type cytokeratin status. This observation gives another difficulty in establishing an easy and simple method of identification of tumors that have a basal-like signature in microarray analysis.