Quantitative real-time PCR analysis and microarray-based RNA expression of HER2 in relation to outcome

Our aim was to use quantitative real-time PCR (Q-PCR) and RNA expression profiles (RNA-EPs) to investigate HER2 status in relation to outcome.

Cut-off levels for Q-PCR and RNA-EP were established in relation to immunohistochemistry (IHC) validated by FISH in a test set of frozen tissue samples from 40 primary breast cancers. The HER2 status was subsequently studied in another validation set of 306 tumors, where Q-PCR and RNA-EP results were compared with previously carried out IHC that we had validated by chromogenic in situ hybridization (CISH).

Q-PCR and RNA-EP offered similar sensitivity (90% versus 77%), specificity (93% versus 95%), and negative (99% versus 98%) and positive (63% versus 61%) predictive values for HER2 determinations. Analyses of relapse-free survival (RFS) and overall survival on the basis of 5 and 10 years of follow-up indicated equivalent hazard ratios for all three techniques. In contrast to IHC/CISH, both Q-PCR and RNA-EP analyses of HER2 also gave statistically significant results regarding RFS and breast cancer-corrected survival after 10 years of follow-up.

The use of RNA-EP and Q-PCR to analyze HER2 in frozen and formalin-fixed breast cancer samples may be an alternate approach to IHC in combination with FISH/CISH.