871P - Detection of circulating tumor DNA in operable loco-regionally advanced HPV-negative head and neck squamous cell carcinoma

Background

Despite multimodal treatment, half of the patients with operable loco-regionally advanced HPV-negative head and neck squamous cell carcinoma (HNSCC) will relapse. We aimed to evaluate the detection rate of circulating tumor DNA (ctDNA) before and after surgery and its correlation with baseline characteristics.

Methods

This prospective study (NCT03896412) included forty patients with HPV-negative HNSCC, treated by curative intent for a locally advanced (T3/T4 or node positive (N+)) by surgery followed by radio or radiochemotherapy. We looked for genes alteration on tumor tissue and ctDNA. Blood sampling was performed right before and the day after surgery. We used a custom panel targeting all exons of genes AJUBA, TP53, CASP8, PIK3CA, NOTCH1, HRAS, CDKN2A, FAT1, NFE2L2, NSD1 and EPHA2. Analyses were performed with two bioinformatics pipelines; CLC software by Qiagen and a homemade pipeline. A pathogenic variant was considered if present in both pipelines. The sequencing depth was 2000X for tumors and 9000X for ctDNA.

Results

Among the 40 patients, 18 (45%) had a T4 stage disease, 25 (62.5%) a N+ disease. All patients underwent surgery. Regarding tumors, 36/40 (90%) had enough DNA amount and quality for NGS analysis. At least one pathogenic variant was identified in 30/36 tumors (83.3%): TP53 was mutated in most of cases (93.3%), PIK3CA mutated in 8.3%, FAT1 mutated in 5.6% and CASP8 mutated in 2.8% of patients. No pathogen variant were found for AJUBA, NOTCH1, HRAS, CDKN2A, NFE2L2, NSD1 and EPHA2. Analysis of ctDNA before surgery revealed at least one pathogenic variant in 8 patients. In all cases, the variant in ctDNA was detected in the matched tumor. For 3 patients, multiple variants were detected in ctDNA. Allelic frequency in ctDNA varied from 0.33% to 29.95%. Cell free DNA (cfDNA) rate was significantly increased after surgery (11.24 ng/mL vs 14.70 ng/mL, p<0.0001). Analysis of ctDNA the day after surgery did not identify any pathogenic variant.

Conclusions

In this cohort of locally advanced HPV-negative HNSCC, our NGS custom panel identified pathogenic variants in 83.3% of the tumors, but only in 20 % of preoperative ctDNA samples. Despite cfDNA increase after surgery, no pathogenic variant was identified in blood samples.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

Centre Henri Becquerel.

Funding

Cancéropole Nord Ouest.

Disclosure

All authors have declared no conflicts of interest.