358 Background: In resectable GAC/GEJAC, MSI status is associated with better survival and potential lack of benefit from chemotherapy. Given the high responsiveness of MSI tumors to immunotherapy, neoadjuvant or definitive dual CTLA-4/PD(L)-1 inhibition may allow omission of chemotherapy or surgery. Methods: INFINITY is a multicentre, single-arm, multi-cohort phase II trial (NCT04817826) investigating the activity and safety of tremelimumab+durvalumab as neoadjuvant (Cohort 1) or definitive (Cohort 2) treatment for MSI, mismatch repair deficient (dMMR) and EBV-negative resectable GAC/GEJAC. In Cohort 1, patients (pts) received a 12-week treatment with single high dose tremelimumab 300 mg and durvalumab 1500 mg q4 weeks (T300/D) for 3 cycles followed by surgery. The primary endpoint was pCR rate (ypT0N0) with negative ctDNA after T300/D. Secondary endpoints: disease-free survival, overall survival, quality of life. Exploratory: correlation of pCR with clinical variables, PDL-1 CPS assessed by IHC 22C3, tumor mutational burden (TMB) by Foundation One, liquid biopsies and other biomarkers. Cohort 2 investigates non operative management after same treatment regimen. Results: Overall, 18 pts with MSI/dMMR resectable cT2-4 any N GAC/GEJAC were recruited in Cohort 1. One withdrew consent and 2 achieved a complete clinical-pathological response at radiology and endoscopy (ongoing) and refused surgery. Among 15 evaluable patients, 1 had disease progression and 14 underwent resection. pCR rate was 60% (9/15) and major-complete pathological response (<10% viable cells) was 80%. All pts with pCR had negative ctDNA status pre-surgery. pCR rate was 1/6 (17%) in T4 vs 8/9 (89%) in T2-3 tumors (p=0.011), whereas no correlation was found with baseline N status. PDL-1 CPS was not associated with outcomes and TMB had a non-significant trend of correlation with pCR (median TMB 26 in non-pCR vs 40 in pCR group, p=0.2). Grade≥3 immune-related AEs occurred in 3 pts of safety population (n=18): colitis, pneumonitis, liver toxicity, all resolved with high dose steroids and did not impair surgery. Two pts died after surgery for other reasons than disease or AEs, whereas no disease relapses were observed in remaining pts. QoL and additional translational analyses on RNA-seq, digital spatial profiling and ctDNA monitoring will be presented. Conclusions: Pre-operative T300/D for 3 months was safe and provided promising proof of efficacy in MSI, dMMR GAC/GEJAC pts. These results open the way to investigate NOM in pts with clinical, pathological and molecular (ctDNA minimal residual disease) complete response after T300/D. Enrollment in Cohort 2 has started after IDMC evaluation and protocol. amendment to include only pts with cT2-3 tumors confirmed at staging laparoscopy. Clinical trial information: NCT04817826 .
LBA3513 Background: The combination of capecitabine plus long course radiotherapy (RT) is the standard preoperative therapy in cT3-4 cN+ rectal cancer. pathologic complete remission (pCR) can be considered as surrogate endpoint of efficacy of treatment in terms of disease-free survival (DFS). Preclinical data points heavily toward a strong synergy between RT and immune treatments. Methods: This is a prospective phase II, open label, single arm, multicentre study in patient with locally advanced rectal cancer who receive standard concomitant CT/RT therapy (825 mg/m2 twice daily capecitabine every day and 5040 cGy radiotherapy for 5 days per week for 5 weeks) followed by durvalumab (1500 mg Q4W for 3 administrations). Surgery is performed after 10-12 weeks from neoadjuvant therapy. The primary endpoint is the proportion of pCRs after at least 1 cycle of durvalumab; secondary endpoints are the proportion of clinical complete remissions (cCRs) after at least 1 cycle of durvalumab, the proportion of adverse and serious adverse events (NCI CTCAE v5.0). The sample size has been estimated by using the optimal Simon’s two-stage design assuming a null pCR proportion of 0.15 and an alternative pCR percentage of 0.30 (alpha = 0.05, power = 0.80). If more than 4 pCRs were observed in the first 19 enrolled patients, 36 additional patients were to be accrued for a total of 55 evaluable patients. The null hypothesis is rejected if ≥ 13 pCRs are observed in 55 patients. Results: Between November 2019 and August 2021, 60 patients were accrued, of which 55 were evaluable for study objectives. Fifty-two of 55 treated patients received all 3 infusions of durvalumab. After treatment, a clinical response percentage of 81.8% was observed; 3 patients had progression of disease due to local and/or metastases before surgical intervention. Eighteen patients achieved complete pathological response (32.7%), confirmed by central revision. Near complete regression, moderate and minimal regression were observed in 14 (25.5%), 9 (16.4%) and 11 (20.0%) patients respectively. Regarding toxicity, 23 patients (41.8%) had adverse events (AEs) related to durvalumab treatment. Two patients (1.8%) discontinued durvalumab for toxicity. Grade 3 AEs occurred in 4 (7.3%) patients (diarrhea, skin toxicity, transaminase increase, lipase increase and pancolitis). No Grade 4 toxicity was observed. In 20 patients (36.4%) G1-2 AEs related to durvalumab were observed. The most common were endocrine toxicity (hyper/hypo-thyroidism), dermatologic toxicity (skin rash) and gastrointestinal toxicity (transaminase increase, nausea, diarrhea, constipation). Conclusions: This study met its primary endpoint showing a promising activity of neoadjuvant chemo-radiotherapy plus durvalumab in terms of pCR rate and a safe toxicity profile. Clinical trial information: NCT04083365.
3534 Background: Gut microbiome has emerged as a biomarker of clinical benefit to immune-checkpoint inhibitors (ICI) but no data are available in metastatic colorectal cancer (mCRC). The AtezoTRIBE study demonstrated that the addition of atezolizumab (atezo) to FOLFOXIRI plus bevacizumab (bev) prolongs progression-free survival (PFS), but this benefit is limited for patients with proficient mismatch repair (pMMR) tumors. Here, we aimed at investigating the potential predictive role of microbiome in identifying mCRC patients able to achieve benefit from ICI. Methods: AtezoTRIBE was a phase II trial in which 218 mCRC patients, unselected for MMR status, were randomized 1:2 to receive first-line FOLFOXIRI/bev (arm A) or FOLFOXIRI/bev/atezo (arm B). Stools were prospectively collected. Metagenomic (MG) data from whole genome sequencing (WGS) at level of species genome bins (SGBs) were analysed by linear models corrected for clinical and tumor-related parameters and fold-ratios. We defined as responders (R) those patients who experienced a PFS ≥ 12 months. Results: Stool samples were collected at baseline for 171 (78%) patients (55 in arm A and 116 in arm B) but only 163 were available for MG. Patients with deficient MMR (dMMR) tumors (N = 10) showed significantly lower MG diversity than pMMR ones (N = 148) harboring oral bacteria and pathobionts whose intrinsic immunogenicity has not been demonstrated. Regarding pMMR mCRC patients, baseline microbiome composition was not significantly different according to the treatment arm. The microbiome diversity was not significantly different between R and not-R in both arms, but specific immunogenic SGBs (Lachnospiraceae family members) were over-represented in R treated in arm B. Veillonellaceae and pathobionts were associated with poor prognosis and/or differential benefit from the addition of atezo. Fusobacterium nucleatum was associated with a poor prognosis, also in arm B. Conclusions: This is the largest prospective analysis showing that SGBs may be useful as a biomarker of potential benefit or detrimental effect from atezo in pMMR mCRC patients. Our results prompt the design of microbiota-centered diagnostic tests to identify pMMR mCRC patients more likely to benefit from ICI-based therapeutic strategies. Clinical trial information: NCT03721653 .
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