Comparison of protein expression between formalin-fixed core-cut biopsies and surgical excision specimens using a novel multiplex approach.

PURPOSE: We evaluated whether multiplex protein quantification using antibody bar-coding with photocleavable oligonucleotides (NanoString) can be applied to evaluate protein expression in breast cancer FFPE specimens. We also assessed whether diagnostic core-cuts fixed immediately at time of procedures and surgical excision sections from routinely fixed breast cancers are affected by the same fixation related differences noted using immunohistochemistry (IHC).

METHODS: The expression of 26 proteins was analysed using NanoString technology in 16 pairs of FFPE breast cancer core-cuts and surgical excisions. The measurements yielded were compared with those by IHC on Ki67, PgR and HER2 biomarkers and pAKT and pERK1/2 phosphorylated proteins.

RESULTS: When considered irrespective of sample type, expression measured by the two methods was strongly correlated for all markers (p < 0.001; ρ = 0.69-0.88). When core-cuts and excisions were evaluated separately, the correlations between NanoString and IHC were weaker but significant except for pAKT in excisions. Surgical excisions showed lower levels of 8/12 phosphoproteins and higher levels of 4/13 non-phosphorylated proteins in comparison to core-cuts (p < 0.01). Reduced p4EBP1, pAMPKa, pRPS6 and pRAF1 immunogenicity in excisions was correlated with tumour size and mastectomy specimens showed lower p4EBP1 and pRPS6 expression than lumpectomy (p < 0.05).

CONCLUSIONS: Our study supports the validity of the new multiplex approach to protein analysis but indicates that, as with IHC, caution is necessary for the analysis in excisions particularly of phosphoproteins. The specimen type, tumour size and surgery type may lead to biases in the quantitative analysis of many proteins of biologic and clinical interest in excision specimens.