Is the primary tumor location (PTL) associated with differential gene expression profiles in patients with metastatic colorectal cancer (mCRC)? Analysis of the FIRE1-trial.

Abstract

598 Background: Site-differential molecular characteristics of PTL as well as its influence on overall survival have been reported. In our study, we investigated the association of PTL with gene- and pathway-wise RNA expression as well as its representation in RAS mutational status subgroups. Methods: The phase-III-trial FIRE-1 compared the efficacy of FuFIRI and mIROX in patients with mCRC. Formalin-fixed, paraffin-embedded pretreatment samples from 166 FIRE-I patients were collected. The splenic flexure was used for differentiation between left colon cancer (LC) and right colon cancer (RC). RAS mutated PTs (RASmut) had PCR confirmed mutations in KRAS gene (Exon 2, 3, or 4) or in NRAS gene (Exon 2, 3, or 4). RNA expression profiling used the nCounter(R) PanCancer Pathways Panel including DNA damage control and TGF-β. We also studied a set of selected genes (Aprataxin, AREG, CD3EAP, CES1, CES2, CMPK1, DPD, DUT, ERCC1, ERCC5, EREG, FGF2, GSTP1, KLC3, MTHFR, PPP1R13L, RCC1, TOPO1, TP, TS, and UGT1A1). The gene-wise analyses used Limma and the permutated t-test with appropriate multiple testing adjustment. Holistic pathway investigation used GlobalAncova and the global tests. RAS mutation status and its correlation with tumor side were included as factors in both analyses. Additionally, gene- and pathway-wise analyses were performed in RASmut and RASWTsubgroups. Results: A total of 83 (50%) of 166 patients had any RAS mutation. A total of 28 (17%) patients had PTs on the right side and 13 of those (46%) were RASmut. The top ten differentially expressed genes between LC and RC are MMP9, ERCC3, MAP3K1, RRAS2, SOCS3, RB1, TGFβ1, LEFTY1, NKD1, and CDC25B (unadjusted p-values < 0.005). Potential enrichment in the DNA damage control pathway was found (p = 0.008). The RAS subgroup analyses showed a non-overlapping top ten list. Side specific effects may exist for the TGF-β pathway and the selected gene set in RASWTpatients. Conclusions: No strong association between PTL and gene expression showed up in mCRC tumors nor RAS subgroups. Potentially differential gene expression may exist for specific genes, two pathways and our selected gene set.