Primary results of the ICONIC phase 2 trial of perioperative FLOT plus avelumab (FLOT-A) in operable oesophagogastric adenocarcinoma (OGA).

446 Background: ICONIC evaluated 4+4 cycles of FLOT-A (2-weekly standard FLOT with 10mg/kg of the anti-PDL1 antibody avelumab) for perioperative treatment of early-stage OGA. We report R0 resection rates, pathologic complete response rates (pCR), pathologic tumour regression grades (TRG) according to Mandard classification and progression free survival (PFS) data in the modified intention to treat population (mITT), and translational analyses. Methods: ICONIC is a single-arm phase II trial of FLOT-A in patients (pts) with ≥cT2-4 or N+ OGA. The pCR rate in surgical specimens was the primary endpoint. Response evaluation according to Mandard, R0 rates and PFS were among secondary endpoints. PD-L1 expression was assessed according to the combined positive score (CPS) with the 22C3 pharmDx kit. Results: The trial closed early after the pCR rate was 15% (95% CI: 49%-83%) once 34 pts in the mITT population (defined as pts who had 1-4 cycles FLOT-A and surgery) as the pre-specified aim to demonstrate a pCR rate of 25% in 40 pts was unlikely to be met. Baseline characteristics of the mITT population were: median age 64y, 79% male, 79% OG junction, 6% oesophageal, 15% stomach, 65% poorly differentiated, 79% T3/4, 59% N+. 91% of pts received all 4 pre-operative cycles and 97% of pts achieved R0 resections. PDL1 CPS ≥1 and CPS ≥5 were nevertheless associated with increased TRG3 and decreased TRG4/5 rates. 3/34 pts (9%) had hypermutated/MMRd tumours and after their exclusion, the association of higher CPS with better TRG3 and decreased TRG4/5 remained. With a median follow up duration of 15.8 months the 12-month PFS was 93.1% (95% CI: 75.1%-98.2%) which is promising compared to historic results with peri-operative FLOT. Conclusions: Although FLOT-A failed to increase pCR rates to 25%, there is a trend towards higher TRG3 and lower TRG4/5 in pts with PDL1 CPS≥1 and CPS≥5 and promising PFS indicate activity of immunotherapy in combination with FLOT chemotherapy. Translational and biomarker analyses by exome- and RNA-sequencing, and multiplex immune cell staining are ongoing and will be reported. Clinical trial information: NCT03399071 . [Table: see text]