Background: In the phase II CheckMate-142 trial, NIVO + low-dose IPI (1 mg/kg) provided meaningful clinical benefit in previously treated MSI-H/dMMR mCRC pts after a median follow-up of 13.4 mo. Here, we present long-term follow-up (median 25.4 mo) of these pts. Methods: Pts received NIVO 3 mg/kg + low-dose IPI Q3W (4 doses) followed by NIVO 3 mg/kg Q2W until disease progression. Primary endpoint was investigator (INV)-assessed objective response rate (ORR; RECIST v1.1). Results: Of 119 treated pts, 76% had ≥ 2 prior lines of therapy. ORR and disease control rates (DCR) were 58 and 81%, respectively (Table). Complete response (CR) rate increased with long-term follow-up from 3 (13.4 mo) to 6% (25.4 mo). Median duration of response (DOR) was not reached, with 68% of responses ongoing at data cutoff. At 24 mo, progression-free survival (PFS) and overall survival (OS) rates were 60 and 74%, respectively; OS rates were 96, 56, and 29% in pts with CR or partial response (PR), stable disease (SD), and progressive disease (PD), respectively. Grade 3–4 treatment-related adverse events (TRAEs) occurred in 31% of pts; 10% (grade 3–4) and 13% (any grade) of pts had TRAEs leading to discontinuation. Conclusions: Long-term follow-up with NIVO + low-dose IPI provides durable clinical benefit with deepening of response and a manageable safety profile with no new safety signals, demonstrating long-term benefit of NIVO + low-dose IPI for previously treated pts with MSI-H/dMMR mCRC. Clinical trial information: NCT02060188

*Median follow-up NE = not estimable NR = not reached