Background: AFP response, defined as a decrease in serum levels of the tumor marker AFP after therapy, may be associated with improved survival of patients (pts) with HCC treated with locoregional or systemic therapy, and high baseline AFP levels may be associated with poor prognosis. In the phase III CELESTIAL trial (NCT01908426), C, an inhibitor of MET, VEGFR, and AXL, significantly improved overall survival (OS) and progression-free survival (PFS) versus P in pts with previously treated advanced HCC. Here we evaluate clinical outcomes with C in CELESTIAL based on AFP response or progression on treatment. Methods: 707 pts were randomized 2:1 to receive C (60 mg daily) or P. Eligible patients had a pathologic diagnosis of HCC, Child-Pugh score A, and ECOG PS ≤ 1. Pts received prior sorafenib and ≤ 2 lines of prior systemic therapy for HCC. Serum AFP levels were measured centrally at baseline and every 8 weeks thereafter. Outcomes were evaluated for pts with baseline AFP ≥ 20 ng/mL based on AFP response ( ≥ 20% decrease from baseline) or progression ( ≥ 20% increase from baseline) at Week 8. This definition of AFP response has been used in previous studies but requires further validation in large prospective studies. Results: Overall, 331 pts (70%) in the C arm and 160 (68%) in the P arm had baseline AFP ≥ 20 ng/mL; among these pts, 236 (71%) and 111 (69%), respectively, were evaluable for AFP response at week 8. Among evaluable pts, 117 pts (50%) in the C arm vs 14 (13%) in the P arm had an AFP response, and 72 (31%) vs 75 (68%) had AFP progression. Median OS with C was 16.1 mo for pts with an AFP response versus 9.1 mo for pts without a response (HR 0.61, 95% CI 0.45-0.84), and median PFS with C was 7.3 mo versus 4.0 mo (HR 0.55, 95% CI 0.41-0.74). For pts with AFP progression, median OS with C was 8.1 mo, and median PFS with C was 3.6 mo. Hazard ratios for OS and PFS with C also favored AFP responders over non-responders when analyzed using best response through week 24. Conclusions: The AFP response rate was higher with C versus P, and AFP response was associated with longer OS and PFS with C for pts with previously treated advanced HCC. On-treatment AFP changes warrant further evaluation as a biomarker of response. Clinical trial information: NCT01908426