Is RECIST-defined progression free-survival a meaningful endpoint in the era of immunotherapy?

488Background: Progression-free survival (PFS) is often used as a primary endpoint in oncology clinical trials as a surrogate for overall survival. Traditionally, the Response Evaluation Criteria in Solid Tumors (RECIST) have defined disease progression as a significant increase in the size of tumor lesions and the development of new lesions. However, some patients starting immunotherapy have shown initial increased size of tumor lesions followed by tumor regression, due to the unique mechanism of action of immunotherapies. This initial “pseudo-progression” could be classified inaccurately as disease progression, as evidenced by benefit from the treatment beyond progression approach (JAMA Oncol 2016). The phase III CheckMate 025 trial of nivolumab versus everolimus in patients with advanced renal cell carcinoma allowed treatment beyond progression if there was investigator-assessed clinical benefit and tolerability. The purpose of our study was to test if treatment duration for an immunotherapy was differ...