Remission
When the signs of cancer have shrunk (partial remission) or disappeared entirely (complete remission). It is not the same as cure, because cells too few to detect may remain.
In blood cancers, complete remission has precise definitions (normal blood counts, fewer than 5% blasts in the marrow) and can be refined by measuring minimal residual disease; in solid tumours the equivalent language is complete or partial response on scans, or 'no evidence of disease' after surgery. Whether a remission becomes a cure is only known with time: for most cancers, five years without recurrence is a reasonable proxy, though late relapses occur in breast cancer and melanoma. Immunotherapy has introduced durable remissions in metastatic disease that behave like cures, and 'functional cure' describes long control without eradication.