From the first reference below: Resection margin or surgical margin as defined by Hinni et al. is any tissue plane where the surgeon's knife meets the patient.[2] During surgical removal, the palpable or visible tumor is resected with a fringe of normal tissue to ensure complete removal of tumor. This mainly depends on surgeon's clinical judgment, interpretations of imaging investigations and preoperative planning of the extent of resection.
"Ved ufrie reseksjonsrender, det vil si hvis histologisk analyse viser at man ikke med sikkerhet har fjernet alt tumorvev under operasjonen, kan kombinert tilleggsbehandling med cellegift og strålebehandling vurderes." https://kreftlex.no/Magesekkreft/ProsedyreFolder/BEHANDLING/...