Clinical response and biomarker analysis of POLARIS-02 a phase II study of toripalimab, a humanized IgG4 mAb against programmed death-1 (PD-1) in patients with metastatic nasopharyngeal carcinoma.

Abstract

6542 Background: Metastatic nasopharyngeal cancer (mNPC) patients progressed after standard therapy have limited treatment options. This study is to evaluate the clinical efficacy and safety of toripalimab in mNPC patients refractory to standard chemotherapy treatment (Clinical trial ID: NCT02915432). Methods: Patients receive 3 mg/kg toripalimab Q2W via IV infusion until disease progression, unacceptable toxicity, or voluntary withdrawal. Clinical response is assessed every 8 weeks according to RECIST v1.1. Tumor PD-L1 expression, plasma EBV titer and other biomarkers will be evaluated for correlation with clinical response. Results: From Dec 2016 to Feb 2019, 190 mNPC patients were enrolled from 17 participating centers in China. The median age was 46 years with 83% male. Patients were heavily pretreated with a median of 2 lines of prior systemic treatments. By the cutoff date of Jan 17, 2020, 97% patients experienced treatment related adverse events (TRAE). Most common TRAE included anemia, hypothyroidism, AST increased, proteinuria and fever. Grade 3+ TRAE occurred in 28% patients. Among 190 patients assessed by Independent Review Committee per RECIST v1.1, 6 CR, 33 PR and 40 SD were observed for an ORR of 20.5% and a DCR of 41.6%. The median DOR was 12.9 months. The median PFS and median OS were 1.9 months and 18.6 months respectively. PD-L1+ patients (n=48) had higher ORR than PD-L1- patients (n=134), 27.1% versus 19.4%. By tumor histology, ORR was higher in keratinizing NPC (n=8) than non-keratinizing NPC (n=168), 62.5% versus 19.0%. 144 patients had valid plasma EBV titer measured every 28 days during the study. An average drop of 101-fold plasma EBV titer from baseline was observed in patients with objective responses. Patients with 2-fold+ drop in plasma EBV titer on day 28 (n=60) went on to have 48.3% ORR and 76.7% DCR, whereas patients with less than 2-fold drop (n=88) had 5.7% ORR and 25.0% DCR. 14 responding patients who later developed progressive disease had at least 2-fold+ increase of plasma EBV tier 3-months (median) before radiographic identification of disease progression. Conclusions: Toripalimab demonstrated encouraging clinical activity with a manageable safety profile in mNPC patients refractory to standard chemotherapy. Patients with 2-fold+ drops in plasma EBV titer on day 28 from baseline had favorable clinical response of 48.3% ORR, which might be used as a predictive biomarker. Clinical trial information: NCT02915432 .