In contrast, 8 patients (colorectal cancer, n = 4; squamous cell head and neck, n = 1; non-squamous head and neck cancer, n = 1; breast, n = 1; NSCLC, n = 1) had PIK3CA E542K or E545K mutations in cfDNA but not in FFPE tumor samples. The gene discussed is PIK3CA; the disease is colorectal cancer.