e17516 Background: Head and Neck Squamous Cell Carcinoma (HNSCC) is an increasingly prevalent disease but effective targeted therapy is lacking. The use of next generation sequencing (NGS) in the identification of novel targets has been suggested as a way to potentially expand therapeutic options and thereby improve outcomes. Methods: Data was collected on patients with recurrent and metastatic (R/M) head and neck cancers who underwent molecular profiling of blood samples utilizing Guardant360, a 70-gene circulating tumor DNA (ctDNA) NGS platform. CtDNA sequencing data was compared to tumor NGS data, when available. Best response to therapy was assessed using RECIST measures. Results: 60 HNSCC patients were evaluated from February 2015 to June 2016. The most common tumor type and histology was oropharyngeal squamous cell carcinoma (n = 21), which was commonly human papillomavirus (HPV) positive (n = 15). Other cancer types included salivary gland and thyroid cancers. The most common mutations identified by ctDNA analysis were TP53 (98%), PIK3CA (43%), NOTCH1 (38%), and ARID1A (36%). These findings were consistent with results from tumor sequencing data (n = 29) where TP53 (48%) and PIK3CA(24%) were also reported with the highest frequency. Importantly, 73% (n = 22) of patients had alterations identified in ctDNA that were not present in tumor specimens. Actionable mutations were identified in 66% of HNSCC and in 50% salivary gland cancer patients. Of patients with actionable mutations, 10% (n = 6) received matched targeted therapy (MTT): 3 (50%) had stable disease (SD), 1 had progressive disease (PD), and 2 were not evaluated. Of those who did not receive targeted therapy (n = 23), 1 (4.3%) patient had a complete response treated with immunotherapy, 11 (47%) had SD, and 11 (47%) had PD. Conclusions: Analysis of ctDNA may play a role in management decisions in R/M HNSCC. The majority of patients had unique mutations identified on ctDNA. The utility of ctDNA NGS and its role in patient management should be explored in future studies.
Next generation sequencing of cell free circulating tumor DNA in blood samples of recurrent and metastatic head and neck cancer patients
