Monitoring C-reactive protein facilitates early discontinuation of immune oncology without compromising outcomes in stage IV non-small cell lung cancer.

e21107 Background: C-Reactive Protein (CRP) is a non-specific inflammatory marker and reflects tissue destruction seen in metastatic cancer (ca). We have observed a tight correlation with CRP trends mirroring ca activity, hence it may prove to be a valuable marker to monitor response to Immuno-Oncology (IO) in non-small cell lung cancer (NSCLC) patients (pts). Once CRP levels stabilized, IO discontinuation was offered, and consenting pts were closely observed. This strategy resulted in shortened IO duration and impressive treatment-free progression-free survival (tf-PFS). We sought to examine the validity of this strategy using the rate of return to any form of ca therapy within 6 months after stopping IO. Methods: We analyzed all pts of a single provider since 2016 with stage IV NSCLC who had CRP checked while on IO, totaling 23 pts. We excluded pts who stopped IO for reasons besides stable CRP values (5 progressed on IO, 3 died while on IO, 1 had side effects, 1 stopped for a clinical trial, 1 opted to complete 2 years of IO, and 2 are still on IO). Of the remaining 10 patient cohort, all pts were males treated at the VA with ages between 56-75 years at diagnosis. 50% of the cohort had adenocarcinoma and 50% had squamous cell carcinoma. Results: Using the CRP trend to shorten the duration of IO resulted in durable drug-free holidays with none of the cohort returning to any form of ca therapy within 6 months and comparable rates of overall survival (OS) despite shorter IO duration. In KEYNOTE-042, the median OS for pts on the pembrolizumab arm was 16.7 months in the overall population and 20 months in the TPS ≥50% subgroup. Pts were treated for up to 35 months. In our cohort, median OS was 38 months, with all pts currently still alive, and median number of doses of IO was 9 cycles, or approximately 7 months. Our pts had ongoing progression free survival (PFS) after stopping treatment, which we report as tf-PFS. The median tf-PFS of our cohort was 23.5 months. Conclusions: In pts with stage IV NSCLC treated with IO, CRP appears promising as a marker to tailor IO therapy addressing tumor and clinical heterogeneity. Responding pts with stable CRP levels can be safely taken off IO. CRP should be monitored with stable values indicating continued PFS. tf-PFS rather than PFS may serve as a surrogate for cure and carries significant impact for pts financially, socially, and psychologically. [Table: see text]