1760P - Impact of adjuvant imatinib on recurrence for neurofibromatosis type 1 (NF1) associated GISTs: An analysis of the RECKGIST cohort from the French NETSARC+ network

Background

Interest of adjuvant imatinib, the standard of care for resected high risk KIT mutated GIST, is unknown for NF1-GISTs. The aim of this study was to determine whether adjuvant imatinib or surveillance had an impact on relapse.

Methods

This retrospective study included consecutive NF1 patients with operated localized GIST, from 2008-2023 in 25 NETSARC+ centers. Survival was evaluated with Kaplan-Meier curves and compared with the LogRank test. To address potential bias, a 1:1 propensity score and inverse probability of treatment weighting (IPTW) matching were performed.

Results

114 patients operated patients were included. Follow up was 6.1 years, median treatment duration was 21 months (IQR 6-36). 50% of patients relapsed in the adjuvant group (AG, n=22) and 6.5% in the surveillance group (SG, n=92). Unmatched analysis of the 10-years relapse free survival (10y-RFS) showed a worse 10y-RFS of the AG: 47.9% (CI95: 23.8-68.6) vs 91.7% (CI95: 80.8-96.5), p<0.001. Groups were similar for gender (p=0.63), age at inclusion (p=0.31), location (intestinal vs gastric, p=0.99), rupture (p=0.16), mutational status (KIT/PDGFRa mutation yes vs no, p=0.20) but different for year of inclusion (p=0.02), largest size (69 vs 48 mm, p=0.03), mitotic count (7 vs 5 mitoses/5mm², p=0.003), Miettinen high (58.8% vs 12.7%, p<0.001), Joensuu high (90.5% vs 44.8%, p=0.002) and RECKGIST C (40% vs 9.9%, p=0.001) scores. IPTW did not properly match patients, as AG remained of worse prognosis. Best 1:1 matching was only possible for 15 patients of each group. After matching, there was no difference for year of inclusion (p=0.14), location (gastric 13.3% vs 20%, p=0.99), mutational status (KIT/PDGFRa 0% vs 7%, p=0.48), largest size (76 vs 53 mm, p=0.48), mitotic count (8 vs 5/5mm², p=0.86) and RECKGIST score C (31% vs 20%, p=0.88) for AG and SG respectively. 10y-RFS were similar between both groups (LogRank, p=0.34), 60.0% (CI95: 31.8-79.7) and 67.9% (CI95: 28.2-88.8) respectively.

Conclusions

There was no sign of efficacy of adjuvant imatinib after surgery after matching, consistent with its known low efficacy in non KIT/PDGFRa mutated GIST, strengthening ESMO guidelines to avoid adjuvant treatment in NF1-GIST.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

CHU Amiens Picardie.

Funding

Has not received any funding.

Disclosure

V. Hautefeuille: Financial Interests, Personal, Invited Speaker: Novartis, Merck, Amgen; Financial Interests, Personal, Advisory Board: AAA, Ipsen, Pierre Fabre; Financial Interests, Institutional, Invited Speaker: Deciphera, Esteve. B. Verret: Financial Interests, Institutional, Invited Speaker: Lilly, Pfizer, Pierre Fabre, Seagen, Daiichi Sankyo, Gilead, Novartis, MSD, AstraZeneca; Financial Interests, Institutional, Advisory Board: Lilly, Daiichi Sankyo, Gilead, Novartis, Owkins, AstraZeneca, MSD, Boehringer Ingelheim. S. Watson: Financial Interests, Personal, Invited Speaker: Deeciphera, AstraZeneca; Financial Interests, Personal, Advisory Board: Deciphera, Boerhinger Ingelheim. N. Penel: Financial Interests, Institutional, Research Grant, Research grant for clinical trials in sarcoma filed: Bayer HealthCare. F. Ghiringhelli: Financial Interests, Personal, Advisory Board: Roche; Financial Interests, Personal, Invited Speaker: Amgen, Merck Serono, MSD. M. Muller: Financial Interests, Institutional, Invited Speaker: Servier. D. Tougeron: Financial Interests, Personal, Advisory Board: AstraZeneca, Sanofi, Amgen, MSD, Roche, Servier, Pierre Fabre, BMS, Bayer; Non-Financial Interests, Member of Board of Directors: Federation francophone de cancerologie digestive. O. Bouche: Financial Interests, Personal, Advisory Board: Amgen, Merck, Apmonia Therapeutics, Deciphera, Astellas, Takeda; Financial Interests, Personal, Invited Speaker: Servier, Pierre Fabre, Bayer. M. Brahmi: Financial Interests, Personal, Advisory Board: Bayer; Financial Interests, Personal, Invited Speaker: Amgen, PharmaMar, Deciphera. All other authors have declared no conflicts of interest.