LAUSR

e14027 Background: A commercial liquid biopsy test was included as an exploratory component of an integrated immunotherapy clinical trial in previously refractory metastatic TNBC patients, combining innate, high-affinity natural killer cell (haNK) therapy with adenoviral and yeast-based vaccines and an IL-15 superagonist (NCT 03387085). The purpose of the study was to assess the utility of cell-free circulating RNA (cfRNA) as a predictor of treatment response. Methods: Blood was drawn from trial participants at baseline and at 2-6 week intervals throughout the treatment protocol. cfRNA and cfDNA were extracted from plasma and tested for analytes by quantitative PCR (qPCR) in a CLIA and CAP certified laboratory. This study is based on the analysis of 18 the cfRNA analytes (AR, PD-L1, CTLA-4, LAG-3, EGFR, HER2, ERCC1, TIM-3, MGMT, RRM1, SLC29A1, TOP1, TOP2A, TOP2B, TUBB3, TYMP, TYMS, XRCC1) in six patients that had at least three testing time points; new patient recruitment and serial testing are ongoing. The relative expression of each RNA analyte was normalized by beta-actin. Tumor size was evaluated by imaging using the RECIST criteria. Results: The amount and variability of cfRNA was positively correlated with the tumor size. As cfRNA quantity and variability increased or decreased, a corresponding increase or decrease in tumor size was observed, respectively. Not all 18 genes showed consistent patterns of change across the six patients, however the average expression and variability of the 18 genes showed evidence of a correlation with tumor size change from baseline (p-values = 0.08 and 0.03, respectively). Only trace levels of PD-L1 expression were observed in all 6 patients at baseline, prior to the initiation of the combination immunotherapy. Among the 5 patients that showed a reduction in tumor size of at least 10%, 4 also showed an associated increase in cfRNA PD-L1 expression from nearly 0 to normalized values between 2.1 and 6.8. Conclusions: Exploratory analysis in an ongoing combination immunotherapy clinical trial for TNBC showed that increasing and decreasing cfRNA levels are correlated with increasing and decreasing tumor size, respectively. Increased PD-L1 cfRNA levels are correlated with beneficial treatment response. Liquid biopsy of cfRNA could provide an effective biomarker of treatment response. Clinical trial information: NCT03387085.