ctDNA detection by droplet digital PCR before treatment. A, HPV E7 ctDNA levels according to FIGO stages (P = Kruskal–Wallis test) and para-aortic (PA) lymph node status (P = Mann–Whitney test). B, Positive correlation between HPV E7 ctDNA level and tumor HPV E7 copy number. Spearman correlation r = 0.39 (P < 0.001). For undetectable HPV ctDNA cases, the points “a,” “b,” “c,” and “d” refer to 5, 6, 3, and 5 tumors, respectively. C, HPV ctDNA levels according to HPV E7 gene and HPV integration site (n = 23). D, ctDNA detection according to HPV E7 gene and PIK3CA mutation (n = 27).