Progressive Disease (PD) is defined as at least a 20% increase in the sum of diameters of target lesions, taking as reference the smallest sum on study (this includes the baseline sum if that is the smallest on study). In addition to the relative increase of 20%, the sum must also demonstrate an absolute increase of at least 5 mm. (Note: the appearance of one or more new lesions is also considered progression).

In most trial protocols, after the observation of PD, by for instance the development of a new lesion, tumor measurements would no longer necessarily be recorded. It is possible that a new lesion is questionable and a decision is made to reevaluate at the next assessment.  Other than that, it is not clear what the purpose of designating a new lesion as target or non-target would be, since a new lesion that is certain, indicated a PD status.