Thus, an extensive fraction of variants, including TP53 mutations in five patients, PIK3CA mutation in patient 1, and a CDKN2A mutation in patient 2, were exclusive for the primary tissues and not found in the corresponding sera, Their low abundances in the circulation could be influenced by several factors, including differences in tumor load, influences of therapy on the presence of cfDNA, or temporal variations of the abundance of cfDNA with respect to the tumor status. The gene discussed is CDKN2A; the disease is neoplasm.