How to interpret the radiological abnormalities that persist after treatment in non-Hodgkin's lymphoma patients?

A complete response (CR) after treatment is usually associated with a longer event-free survival, a longer duration of response, and a longer survival for patients with non-Hodgkin's lymphoma (NHL), but very seldom with a good partial response (PR); cure has only been described in CR patients after the first line of treatment. Thus, the main objective for the treatment must be to achieve a CR in the majority of the patients. Some exceptions have been observed: long time to progression or long time to next treatment in some PR patients with indolent lymphomas; a good PR may be considered for elderly patients, particularly those with an indolent lymphoma; patients with an indolent lymphoma and no adverse prognostic factors may have a delayed treatment. However, defining a CR may be difficult in some patients, particularly those with an aggressive lymphoma and a large tumor mass at diagnosis, who seem to respond very well to the treatment, with the disappearance of all clinical or biological abnormalities but with persistence of some radiological abnormalities. In different retrospective analyses, the percentage of patients with good PR, defined as the persistence of any radiological abnormalities, who did not progress, and their ultimate time to progression, were not different from those observed in patients with a true CR [1, 2]. Recently, international experts gathered to refine the definition of the different events that may occur in lymphoma patients, particularly the criteria defining a complete response and the other responses [3]. Because of this uncertainty in the definition of CR, a new category of response, CRu, was created to reflect the unknown significance of persisting radiological abnormalities in patients who seem otherwise in CR.