LAUSR

230 Background: To determine changes in MRE HCC stiffness as predictor of immunotherapy response in patients with advanced HCC. Methods: This was a prospective, Institutional Review Board approved study of 15 patients with biopsy proven advanced HCC (not amenable to curative therapy), who were to be treated with Pembrolizumab. Eligible patients were > 18 years old with radiographic disease progression/intolerance to sorafenib. All patients had liver MRI with MR Elastography (MRE) and liver biopsy at baseline and at 9 weeks of therapy. HCC stiffness (kilopascals, kPa) was measured on liver MRE elastograms (stiffness maps). Change in HCC stiffness on MRE was compared with overall survival, time to disease progression, and total number of lymphocytes on targeted liver biopsy. Data cutoff date was September 1st 2018. Analysis was performed using descriptive statistics including Spearman correlation ( R), Cox regression, Wilcoxon rank sum test and Fisher’s exact test. Results: Of the initial 15 patients, 4 withdrew from therapy, 1 patient did not undergo MRE scan, and 1 patient had MRE failure. The final 9 patients included 6 men. Median age was 70 years (range, 54-78). Etiology of liver disease was HCV (n = 4) and NASH (n = 5). HCC was moderately differentiated in 8 of 9 patients and well-differentiated in 1 patient. Median overall survival and time to progression were 52 weeks (range, 16-112) and 18 weeks (range, 9-48), respectively. Average non-tumorous liver stiffness was 3.2 kPa (range, 2.1-4.3). No significant change in non-tumor liver stiffness was seen at 9 weeks (p = 0.12). Median baseline tumor stiffness was 4.5 kPa (range, 2.4-7.5). Increase in HCC stiffness at 9 weeks was seen in 5 patients, decrease in 3 patients and no change in 1. Change in HCC stiffness at 9 weeks correlated significantly with overall survival ( R = 0.83), and time to progression ( R = 0.96), (p < 0.05). Nine patients had liver biopsy at baseline and 7 had biopsy at 9 weeks. HCC T lymphocytes on biopsy (n/mm2) significantly correlated with HCC stiffness ( R = 0.79), (p < 0.01). Conclusions: Our pilot data suggests early change in tumor stiffness may help predict better immunotherapy response in patients with advanced HCC.