Genomic and Transcriptomic Determinants of Therapy Resistance and Immune Landscape Evolution during Anti-EGFR Treatment in Colorectal Cancer

Despite biomarker stratification, the anti-EGFR antibody cetuximab is only effective against a subgroup of colorectal cancers (CRCs). This genomic and transcriptomic analysis of the cetuximab resistance landscape in 35 RAS wild-type CRCs identified associations of NF1 and non-canonical RAS/RAF aberrations with primary resistance and validated transcriptomic CRC subtypes as non-genetic predictors of benefit. Sixty-four percent of biopsies with acquired resistance harbored no genetic resistance drivers. Most of these had switched from a cetuximab-sensitive transcriptomic subtype at baseline to a fibroblast- and growth factor-rich subtype at progression. Fibroblast-supernatant conferred cetuximab resistance in vitro, confirming a major role for non-genetic resistance through stromal remodeling. Cetuximab treatment increased cytotoxic immune infiltrates and PD-L1 and LAG3 immune checkpoint expression, potentially providing opportunities to treat cetuximab-resistant CRCs with immunotherapy.M.G., A.Woolston, L.J.B., and B.G. were supported by CRUK, a charitable donation from Tim Morgan, Cancer Genetics UK and the Constance Travis Trust. G.S. was funded by an Institute of Cancer PhD Studentship, R.G.E. by a Spanish Society of Medical Oncology (FSEOM) grant for Translational Research in Reference Centers. The study was also supported by the ICR/RMH NIHR Biomedical Research Center for Cancer, by the CRUK Immunotherapy Accelerator (ICR/RMH, UCL) and by a Wellcome Trust Strategic Grant (105104/Z/14/Z)