Prospective monitoring for immunotherapy by liquid biopsy and signal pathway alterations in head and neck cancers.

e18000 Background: Clinical biomarkers that predict response or prognosis to immune checkpoint inhibitors (ICIs) are unclear in head and neck squamous cell carcinoma (HNSCC). Comprehensive genome profiling (CGP) testing including liquid biopsy using cell-free DNA (cfDNA) has become clinically available; however, CGP testing is approved only once per patient under the Japanese health insurance system. Therefore, whether liquid biopsy is useful for detecting sequential genetic change and disease progression as a real-time monitoring tool is still unknown. This study aims to analyze the cfDNA in the plasm of recurrent or metastatic (R/M) HNSCC patients during ICI therapy. This study was prospectively conducted to examine the relationship between sequential genetic changes and treatment response. Methods: In this prospective study, we examined ten evaluable R/M HNSCC cases treated with ICI monotherapy (nivolumab or pembrolizumab) from October 2020 to December 2023. Blood samples were collected and analyzed using Guardant360 at differing three-time points (0, 4, and 24 weeks or at progressive disease, PD). Results: The ten cases consisted of 5 males and 5 females, with a median age of 71 years old (52-92 years old). Seven patients received pembrolizumab as a first line and three received nivolumab as the second line treatment. The best response to ICI was partial response (PR) in 3 cases , stable disease (SD) in 1 and PD in 6. Three cases discontinued the study at the second point because of the rapid disease progression. Microsatellite status is stable in all cases. Eight of the ten cases had at least one pathogenic mutation, one case had only variants of unknown significance, and one case that had target lesions at lung metastases had none of them through a series of liquid biopsies. The most frequent gene alterations observed were TP53 (60%), TERT promoter (20%), GNAS (20%), and EGFR amplification (20%). In particular, EGFR amplification had emerged at the second point in two PD cases and these patients showed the sensitivity to cetuximab-based therapy at the following treatment line. In all PD cases, the highest variant allele fraction (VAF) was increased at the second point, which might help predict the response to ICI therapy. In one case achieving PR, BRAF mutation had emerged at the second point. Then it was undetectable at the third point with PD, and GNAS mutation was newly detected. In another case, APC inactivation had disappeared at the second point with PR, even though GNAS mutation emerged, and this case maintained the response to ICI. These results suggest that switching the signals in the MAPK or Wnt pathway could impact the response to ICI therapy. Conclusions: The findings of this prospective study demonstrated that the highest VAF alterations and genetic mutations detected by cfDNA analysis could reflect and predict the response to ICI.