Liquid biopsy monitoring uncovers acquired RAS-mediated resistance to cetuximab in a substantial proportion of patients with head and neck squamous cell carcinoma

46% of patients with on-treatment disease progression showed acquired RAS mutations, while no RAS mutations were found in the non-progressive subset of patients, indicating that acquisition of RAS mutant clones correlated significantly with clinical resistance.

RAS mutations account for acquired resistance to EGFR-targeting in a substantial proportion of HNSCC patients, even though these tumors are rarely mutated at baseline.

Dr. Mascha Binder from the Department of Oncology and Hematology with Sections Bone Marrow Transplant and Pneumology, Hubertus Wald Tumorzentrum / University Cancer Center Hamburg, University Medical Center Hamburg, Hamburg, Germany said, "Head and neck squamous cell carcinomas (HNSCC) arising in the larynx, pharynx, oral cavity, paranasal sinuses and nasal cavity are among the most common types of cancers, accounting for almost 60,000 newly diagnosed cases and more than 10,000 estimated deaths per year in the United States alone."

For this reason, colon tumors harboring activating RAS mutations do not respond to EGFR targeting and mutational screening is therefore routinely used for patient selection prior to treatment.

Figure 1: PCR amplification of EGFR and RAS exons for Illumina targeted next generation sequencing. EGFR exon 12, KRAS/NRAS exons 2/3/4 and HRAS exons 2/3 (green) were amplified from tumor tissue of 46 patients, post-cetuximab circulating tumor DNA of 20 patients and from 12 squamous carcinoma cell lines. Illumina-specific sequences for hybridization and sequencing (yellow) as well as patient-specific barcodes (red) were attached in a second PCR step.

A recent series of pivotal studies on mCRC suggested that acquired resistance to cetuximab may not only be mediated by selection of rare RAS mutated subclones but also by acquisition of epitope-modifying EGFR mutations during cetuximab treatment.

To investigate if these or related mechanisms may play a role in cetuximab resistance of HNSCC as well, the authors set out to scan the cetuximab-interacting ectodomain of the EGFR as well as KRAS/NRAS exons 2/3/4 and HRAS exons 2/3 for mutations in a cohort of 46 HNSCC patients by targeted next generation sequencing, 20 of these with available post-cetuximab circulating tumor DNA.

Future studies should quantitatively determine mutational loads that reliably predict the benefit - or lack thereof - from further cetuximab treatment in patients with acquired RAS mutations.

The Binder Research Team concluded, "Taken together, our data suggests that i) RAS mutant subclones can only be found in a minority of HNSCC tumor samples at baseline, but emerge in a substantial proportion of patients during cetuximab treatment, ii) these mutant subclones correlate significantly with disease progression, and iii) may be detectable with state-of-the-art sequencing technology before clinical resistance occurs. Prospectively, determination of such clones may help to tailor anti-EGFR strategies warranting an evaluation in larger prospective clinical trials. More specifically, mutational loads should be defined that reliably predict a lack of response to cetuximab."

Full text - https://doi.org/10.18632/oncotarget.8943

Correspondence to - Mascha Binder - m.binder@uke.de

Keywords - head and neck squamous cell carcinoma (HNSCC), epidermal growth factor receptor (EGFR), RAS, resistance, cetuximab