Complete response (CR) and partial response (PR)
A complete response means every measurable trace of the cancer has disappeared on scans or in the marrow; a partial response means it has shrunk by at least 30% (RECIST) but is still there. Neither is the same as cure: microscopic disease can remain.
Overview
Solid tumour responses are defined by RECIST 1.1 (complete: all target lesions gone and nodes <10 mm; partial: ≥30% decrease in summed diameters; progressive: ≥20% increase or new lesions; stable: neither); lymphoma uses Lugano and PET; leukaemia uses marrow blast count and count recovery (CR, CRi for incomplete recovery); myeloma uses IMWG (stringent CR, VGPR, PR). Complete responses are the strongest single-arm signal and, when durable, drive accelerated approvals; the proportion of complete responders and the depth of response (MRD, ctDNA clearance) increasingly predict long-term outcome. In neoadjuvant settings pathological complete response is judged on the resected specimen, and clinical complete response guides organ preservation.