How would you incorporate ctDNA to follow up a patient status post surgical resection of the primary colon adenocarcinoma and omental deposits after 6 months of FOLFOX? 

This is an excellent question. Can ctDNA add to the treatment algorithm for patients with peritoneal carcinomatosis where imaging frequently underestimates extent of disease? We are virtually in a data-free zone, but one study (Baumgartner, Ann Surg Oncol. 2018) showed that for 59 patients (mainly with appendiceal cancer) the preop positivity rate was only 40%. So, therefore, in this setting one should be wary of false negative results. However if the ctDNA is positive after surgery, then the patient has minimal residual disease (MRD) and this test can be added to the surveillance CT scans. It is unknown whether it is better to treat early or later, but we do know for colon cancer, ctDNA may clear with systemic therapy some of the time. So,...