Tumor's flare-up and patterns of recurrence in patients (pts) with recurrent and/or metastatic (R/M) head and neck squamous cell carcinoma (HNSCC) treated with anti-PD1/PD-L1 inhibitors.

6072Background: About 20% of R/M HNSCC pts have an objective response with anti-PD1/PD-L1 inhibitors after platinum failure. Some pts, however, experience a rapid flare-up during treatment. We evaluated the relationship between a flare-up occurence and the patterns of recurrence in R/M HNSCC pts treated with anti-PD1/PD-L1. Methods: Data from R/M HNSCC pts treated with anti-PD1/PD-L1 in 4 French Cancer Centers between 09/2012 and 09/2015 were retrospectively collected. Pts had an imaging performed at least 2 weeks prior to baseline imaging to estimate tumor growth kinetics (TGK) before and on immunotherapy. TGK before starting immunotherapy (TGKPRE ) was defined as the difference of the sum of the largest diameters of the target lesions (according to RECIST) per unit of time between pre-baseline and baseline imaging, while TGK on immunotherapy (TGKPOST ) was defined as the same difference between baseline and last imaging performed on treatment. The TGK ratio (TGKR ) was defined as TGKPOST / TGKPRE . A fl...