Abstract 1047P
Background
Microsatellite instability (MSI) is a predictive biomarker for response to anti-PD(L)1 immune checkpoint blockers (ICB). We aimed to describe a cohort of MSI pts did not progress within 12 months after ICB initiation.
Methods
We reviewed all pts treated in our institution with ICB (mostly in clinical trials) for a MSI metastatic solid tumor and who did not progress during the first 12 months of treatment. The primary objective was to describe this cohort of pts in terms of duration of treatment, response rate, progression-free survival (PFS) and overall survival (OS).
Results
Between April 2014 to April 2020, 67 MSI pts were treated with an ICB and 35 (52%) received the ICB for more than 12 months without tumor progression. The main characteristics were as follow: 23 (66%) female, median age of 61 years (IQR: 28-74), median number of previous lines 2 (range: 0-5). Most common tumor were colorectal (n=16, 46%) and endometrial cancers (n=8, 23%). Twelve patients (34%) had confirmed Lynch Syndrome (LS). Duration of treatment was predetermined by the clinical trial and was as follow: 12 months (n=6, 17%), 18 months (n=3, 9%), ≥24 months (n=26, 74%). 29/35 pts, (83%) had an objective response; 14 (40%) complete response (CR) and 15 (43%) partial response (PR). The median delays from ICB initiation to response and nadir response were respectively 2.7 months (IQR=2-4, range: 1-12) and 9 months (IQR = 3-20, range: 0 - 30). After a median follow up of 41 months (95%CI: 34 - 48), 6 pts out of 35 (17%) had progressive disease. Those 6 pts had as a best response: stable disease n=3, Partial response n=2, complete response n=1. The median PFS (from starting ICB) and median OS (starting from metastatic setting) were not reached. The 1year(y) and 3y-PFS was 100% and 85% respectively, whereas 1y and 3y - OS was 100% and 94%. No difference in PFS was observed between pts who received 12 vs 24 months of treatment.No significant statistical difference(p=0.485) in PFS at 36 months was observed between pts who receiving 12 vs 24 months of ICB: 90% and 78% respectively.
Conclusions
In our series, MSI patients who do not progress within one year remain progression-free in 85% of cases. Patients with stable disease as the best response appear to be more likely to progress compared to responders. Optimal duration of treatment remains unclear.
Clinical trial identification
Editorial acknowledgement
Legal entity responsible for the study
The authors.
Funding
Has not received any funding.
Disclosure
All authors have declared no conflicts of interest.