To save the patient some toxicity
Now this of course is after some previous chemo and later in treatment.
Here was Dr Pashtoon talking about it
From synopsis
"Kasi also points out the ongoing research evaluating whether ctDNA-negative patients could safely forego the rigors of chemotherapy, thus avoiding its associated toxicities"...
https://www.onclive.com/view/dr-kasi-on-the-p...tal-cancer
Here is another little short Dr. Pashtoon video.
https://www.curetoday.com/shorts/the-hidden-r...al-cancers