Fibroblast Growth Factor Receptor 1 (FGFR1) Amplification Detected by Droplet Digital Polymerase Chain Reaction (ddPCR) Is a Prognostic Factor in Colorectal Cancers

Abstract

Purpose: The purpose of this study was to reveal the clinicopathological characteristics and prognostic implications associated with fibroblast growth factor receptor 1 (FGFR1) amplification in colorectal cancers (CRCs).

Materials and methods: We measured the copy number of FGFR1 by droplet digital polymerase chain reaction (ddPCR), and analyzed the FGFR1 expression by immunohistochemistry, in 764 surgically resected CRCs (SNUH2007 dataset, 384 CRCs; SNUH Folfox dataset, 380 CRCs).

Results: CRCs with ≥ 3.3 copies of the FGFR1 gene were classified as FGFR1 amplified. FGFR1 amplification was found in 10 of the 384 CRCs (2.6%) in the SNUH2007 dataset, and in 28 of the 380 CRCs (7.4%) in the SNUH Folfox dataset. In the SNUH2007 dataset, there was no association between the FGFR1 copy number status and sex, gross appearance, stage, or differentiation. High FGFR1 expression was associated with female sex and KRAS mutation. At the molecular level, FGFR1 amplification was mutually exclusive with BRAF mutation, microsatellite instability, and MLH1 methylation, in both SNUH2007 and SNUH Folfox datasets. Survival analysis revealed that FGFR1 amplification was associated with significantly worse clinical outcome compared with no FGFR1 amplification, in both SNUH2007 and SNUH Folfox datasets. Within the SNUH2007 dataset, CRC patients with high FGFR1 expression had an inferior progression-free survival compared with those with low FGFR1 expression. The FGFR inhibitor, PD173074, repressed the proliferation of a CRC cell line overexpressing FGFR1, but not of cells with FGFR1 amplification.

Conclusion: FGFR1 amplification measured by ddPCR can be a prognostic indicator of poor clinical outcome in patients with CRCs.

Keywords: Colorectal neoplasms; Copy number alteration; Droplet digital polymerase chain reaction; Fibroblast growth factor receptor 1; Prognosis.

Fig. 1.

Mutual exclusivity of fibroblast growth factor receptor 1 (FGFR1) amplification with BRAF mutation, microsatellite instability, MLH1 methylation, and CpG island methylator phenotype (CIMP). (A) SNUH2007 dataset. (B) SNUH Folfox dataset. (C) The Cancer Genome Atlas (TCGA) COADREAD dataset. MSS, microsatellite stable; MSI-L, microsatellite instability low; MSI-H, microsatellite instability high.

Fig. 2.

Kaplan-Meier survival curves. (A) 5-Year progression-free survival (PFS) according to fibroblast growth factor receptor 1 (FGFR1) copy number status in SNUH2007 dataset. (B) 5-Year disease-free survival (DFS) according to FGFR1 copy number status in SNUH Folfox dataset. (C) Overall survival (OS) according to FGFR1 copy number status in The Cancer Genome Atlas (TCGA) COADREAD dataset.

Fig. 3.

Cell viability assay using fibroblast growth factor receptor (FGFR) inhibitor, PD173074, in five colorectal cancer cell lines. (A) Copy number of FGFR1 measured by droplet digital polymerase chain reaction. (B) Western blot analysis of FGFR1 protein. (C) Dose-response curves to PD173074. (D) Summary of cell viability assay.