HGSOC is an ideal cancer type in which to explore the clinical utility of ctDNA for response monitoring during treatment in comparison to a clinically accepted biomarker of response, as >99% of cases show mutations in TP53 [23–25] and >90% of advanced HGSOC cases express the serum protein tumour marker CA-125 [26,27]. The gene discussed is TP53; the disease is neoplasm.