Lok – Advisory Committees or Review Panels: Gilead, Immune Targeting System, MedImmune, Arrowhead, Bayer, GSK, Janssen, Novartis, ISIS, Tekmira; Grant/Research Support: Abbott, BMS, Gilead, Merck, Roche, Boehringer The following people have nothing to disclose: Jocelyn Woog, Ajitha Manna-lithara Background Flares during NA therapy are usually associated with antiviral resistance or cessation of therapy. Since ETV resistance is rare and therapy is rarely stopped, we

investigated the frequency and outcome of flares during ETV therapy in CHB. Methods All HBV monoinfected patients treated with ETV from

11 large European centers (VIRGIL Study Group) were studied. Flares were defined as an ALT level Lorlatinib mouse >3× compared to baseline with an absolute ALT level > 3×ULN. Results 733 patients were treated for a median of 168 (IQR 84-213) weeks with ETV monotherapy. Nineteen patients (3%) developed a flare after a median of 26 (10-83) weeks. None of the patients developed genotypic c-Met inhibitor resistance and in only one case non-compliance was documented. Flares were relatively mild with a median ALT peak of 7.3×ULN (IQR 4.5-10-1). Among patients with flares, one developed HBeAg seroconversion, and one lost HBeAg. Baseline HBeAg status (HR 2.91, 95%CI 1.17-7.23, p=0.02), HBV DNA (HR 1.31, 95%CI 1.06-1.63, p=0.01), platelet count (HR 1.0, 95%CI 0.98-1.00, p=0.04) and albumin (HR 0.91, 95%CI 0.84-0.99, p=0.03) were associated with development of a flare. Nine patients (47%) had a flare during decline of HBV 上海皓元 DNA, three

patients (16%) with a stable HBV DNA and seven (37%) with an increase of HBV DNA. Flares during a decline of HBV DNA occurred after a median of 10 weeks (IQR 4-21), which was significantly earlier compared to flares during a stable or increase in HBV DNA (76 weeks, IQR 29-149) (p<0.001). Conclusion Flares during ETV are rare. Flares in patients occurring before week 26 of therapy were almost exclusively present during continued decline of HBV DNA. In these patients ETV can be continued under strict monitoring as the majority have a good biochemical- and virologic outcome. Disclosures: Ivana Carey – Grant/Research Support: Gilead, BMS, Roche; Speaking and Teaching: BMS Ashley S.