397P R-IMMUNE interim analysis: A phase Ib/II study to evaluate safety and efficacy of atezolizumab combined with radio-chemotherapy in a preoperative setting for patients with localized rectal cancer

Background Radiotherapy association with immunotherapy has a strong rationale. This study evaluates this combination before surgery in locally advanced rectal cancer (RC). Methods R-IMMUNE (NCT03127007), a multicentric phase Ib/II prospective trial includes patients with stage II/III RC treated with a preoperative combination of radio-chemotherapy (45-50 Gy/25 fractions, 5FU 225 mg/m2/d, 5d/w from week 1-5) + atezolizumab 1200 mg/infusion (ATZ). The phase Ib had a 3+3 design with a safety period up to surgery and evaluated a single infusion of ATZ at week 3. The phase II, in progress, evaluates 4 infusions of ATZ at weeks 3, 6, 9 and 12. Surgery is planned at week 15. Primary objectives are safety and efficacy based on pathological complete response rate (pCR). Based on a 2-stage Simon design, 36 patients are needed in the phase II to detect a pCR rate increase from 15% to 35% (α = 0.1 and β = 0.1). At least 4 pCRs must be observed among 19 patients treated in the 1st stage to move the 2nd stage. Results This analysis concerns 26 patients treated with the study treatment (median age 66 y-old, 48% male, 88% stage III). Safety was evaluated in 6 patients from phase Ib and 20 from phase II. Overall, 151 AEs were reported and 20 (13%) were grade 3-4 on 9/26 patients, including 2/20 (10%) anastomotic leakage/infections, 4/20 (20%) urinary infections, 1/20 (5%) renal function impairment and 1/20 (5%) immune thrombocytopenia. Three grade 2 immune endocrine disorders were observed. Efficacy was evaluable on 25/26 patients after 1 exclusion for inclusion criteria deviation. Four among 19 patients included in the 1st stage of phase II had a pCR. Overall, 6/25 (24%) pCRs were observed. Conclusions R-IMMUNE interim analysis reveals an acceptable safety profile. Observed pCR rate until now supports the pursuit of the trial. Clinical trial identification NCT03127007