An analysis by Porter et al. of ctDNA from 60 patients with HNSCC showed that TP53 (68%), PIK3CA (34%), NOTCH1 (20%), and ARID1A (15%) were the most frequent mutations, consistent with tumor sequencing data showing that TP53 (48%) and PIK3CA (24%) were the most common mutations [66]. Here, PIK3CA is linked to head and neck squamous cell carcinoma.