Ambrosini, Margherita

Background Immune checkpoint inhibitors (ICIs) are recommended to treat patients with deficient mismatch repair/microsatellite instability high (dMMR/MSI-H) metastatic colorectal cancer (mCRC). Pivotal trials have fixed a maximum ICI duration of 2 years, without a compelling rationale. A shorter treatment duration has the potential to improve patients' quality of life and reduce both toxicity and cost without compromising efficacy. Here we examine whether early treatment discontinuation (ETD) before 13 months in patients without progressive disease (PD) can lead to similar long-term disease control compared with a longer treatment duration (LTD). Methods To assess whether ETD is associated with similar outcomes compared with LTD, we assembled an international cohort of patients with dMMR/MSI-H mCRC treated with ICIs who stopped treatment for a reason other than PD within 395 days (ETD group) and compared them to those who continued for >395 days (LTD group). Outcomes were adjusted for patient/tumor characteristics. Primary endpoint was progression-free survival (PFS) and secondary endpoints were objective response rate (ORR), overall survival (OS) and safety. Results Of 976 patients, 137 and 394 were allocated to the ETD and LTD groups, respectively. In the ETD group, treatment was discontinued due to toxicity (n=56), objective response (n=43), surgery (n=28), patient decision (n=2) or other reasons (n=8). Baseline characteristics were well balanced between the two groups: 22% in both groups received both anti-programmed death-(ligand) 1 (anti-PD-(L)1) + anti-cytotoxic T-lymphocyte antigen-4 (anti-CTLA-4); all others received anti-PD-(L)1 monotherapy. ORR to ICIs was 81% in both groups. Median duration of treatment was ~7 months in the ETD and ~24 months in the LTD group. After a median follow-up of 44 months (IQR: 30–67), similar PFS (HR: 0.92, 95% CI: 0.60 to 1.40, p=0.69) and OS (HR: 1.15, 95% CI: 0.66 to 1.99, p=0.62) from the start of ICIs were observed in ETD and LTD patients. In the ETD group, 28 (20%) patients had a PFS event and 9 restarted ICIs with a disease control rate of 66%. Conclusions In our international series of dMMR/MSI-H mCRC, ETD of ICIs in the absence of PD did not seem detrimental in terms of PFS and OS compared with continuing treatment beyond 1 year. Randomized clinical trials to compare short and long treatment duration are now warranted.

Abstract Purpose: Microsatellite instability (MSI) is currently the only predictive biomarker of efficacy of immune checkpoint inhibitors (ICI) in metastatic colorectal cancers (mCRC). However, 10% to 40% of patients with MSI mCRC will experience a primary resistance to ICI. Experimental Design: In two cohorts of patients with MSI mCRC treated with ICI (exploratory, N = 103; validation, N = 35), 3′ RNA sequencing was performed from primary tumors. Previously described single-cell transcriptomic signatures of tumor microenvironment (TME) were analyzed. Results: In the exploratory cohort, the unsupervised clustering allowed the identification of three clusters of tumors with distinct transcriptional profiles: cluster A (“stromalHIGH-proliferationLOW”), cluster B (“stromalHIGH-proliferationMED”), and cluster C (“stromalLOW-proliferationHIGH”), with an enrichment of patients progressing at first disease assessment under ICI in cluster A (30% vs. 12% in cluster B and 8.1% in cluster C; P = 0.074). Progression-free survival (PFS) was also significantly shorter in patients belonging to cluster A, compared with clusters B or C (P < 0.001) with 2-year PFS rates of 33.5%, 80.5%, and 78.3%, respectively. In multivariate analysis, PFS was still significantly longer in patients belonging to cluster B [HR, 0.19; 95% confidence interval (CI), 0.08–0.45; P < 0.001] and cluster C (HR, 0.25; 95% CI, 0.10–0.59; P = 0.02), compared with patients belonging to cluster A. The association of this clustering with PFS under ICI was confirmed in the validation cohort. PFS related to non–ICI-based regimens was not significantly different according to cluster. Conclusions: This unsupervised transcriptomic classification identified three groups of MSI mCRCs with different compositions of TME cells and proliferative capacities of TME/tumor cells. The “stromalHIGH-proliferationLOW” cluster is associated with a poorer prognosis with ICI treatment.