It is unclear if this is useful especially if asymptomatic from the primary/metastatic sites. The question is being assessed by ECOG/ACRIN in an ongoing randomized trial. The schema may be helpful. https://clinicaltrials.gov/ct2/show/NCT04248452 

I have offered to two patients, both of whom had non-regional lymph node disease extending down the retroperitoneum making them M1, who had no evidence of progression after a few months of multiagent chemotherapy. I would continue to consider in that clinical scenario, treating as a definitive case ...

I have treated in a related scenario before. The patient had a brain-only oligometastasis which we treated with radiosurgery, and then we performed definitive chemo-radiation for the primary esophageal adenocarcinoma. I think the chemo-RT was done after he got induction chemo with FLOT, and he had n...