Does ctDNA play a “surveillance” role in advanced biliary tract cancers during active therapy assessing response and/or defining relapsing disease?

I do not routinely measure ctDNA in biliary tract cancers to assess response (I do use tumor markers and a good cross-sectional imaging modality such as CT or MRI, however).

The investigators on the TOPAZ-1 study have published their work with ctDNA and it does correlate with responders but it is un...