Jeffrey Weber, MD, PhD
Most patients who appear to progress after they begin receiving anticancer immunotherapy will never exhibit a response to therapy. They will continue to progress, just as quickly as they would with no treatment and just as predicted by the Response Evaluation Criteria in Standard Tumors (RECIST) that have long guided clinical trial evaluations and treatment decisions. The trajectory is different, however, for a small minority of patients.
“I’m more concerned about individual practitioners stopping treatment too early,” Weber added. “The assumption that any lesion growth or new lesion signals the failure of one treatment and the need for another has been around for decades. It is a fundamental assumption of RECIST, and that assumption appeared fully justified until immunotherapy came along. I suspect that most practitioners still abide by it for the most part and that it will take some time for the ideas that underlie irRC to be broadly accepted.”
The Start of the IRRC
RECIST and irRC differ in many particulars, but the most important conceptual differences probably lie in their methods for measuring and their timetables for conceding disease progression. Any new lesions or significant growth in 5 or fewer carefully tracked “target lesions” constitutes progression under RECIST. The irRC, on the other hand, is more concerned with total tumor burden. It calls on investigators to track up to 15 lesions, and if the shrinkage of some lesions equals or exceeds growth elsewhere—even if that growth involves totally new lesions—irRC reports stable disease (SD) or responsive disease.
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