Oligometastatic gastrointestinal stromal tumor: Association between treatment type, metastatic pattern, and survival.

e23522 Background: Treatment of oligometastatic gastrointestinal stromal tumor (GIST), defined as the presence of no more than five metastases in a single organ, is challenging, with site of metastases and patient status largely dictating treatment strategies, which inherently prevents this disease from having a definitive treatment plan and outlook of prognosis. The diverse nature of oligometastatic GIST prompted us to study whether overall survival (OS) differs between sites of metastases and type of treatment received. Methods: In this single-center retrospective study, we queried our cancer registry database for subjects with biopsy-proven GIST between January 2011 and December 2021, to include subjects with oligometastatic disease. Data regarding genetic testing, sites of metastases, treatment received, and OS were collected. Association between treatment received and sites of metastases was assessed with Chi-square test. OS curves for most common sites of metastases and treatment types were estimated using Kaplan-Meier curves and compared via log-rank test. Mantel-Haenszel test was used to calculate hazard ratios (HR) between OS with sites of metastases and treatment types. Results: Of291 subjects with GIST in our cancer registry, 49 (17%) had oligometastatic disease (median age: 59 years, 27/22 M/F; median OS: 7.6 years). Most common mutation was KIT exon 11 (32/44 subjects for which KIT status was available), followed by KIT exon 9 (4/44 subjects for which KIT status was available) PDGFRA (4/28 for which PDGFRA status was available), ATM and PIK3CA (3/23 for which next-generation sequencing was performed). Sites of oligometastatic disease included: liver (28/49, 57%), peritoneum (16/49,33%), stomach (2/49,4%), lung, ovaries, and lymph nodes (1/49,2% each). Treatment strategies included: surgery plus systemic therapy (23/49,47%), systemic therapy alone (18/49,37%), external radiation (2/49, 4%), ablation/embolization (2/49,4%), and no treatment (2/49,4%). Subjects with peritoneal oligometastases were more commonly treated with surgery plus systemic therapy compared to liver oligometastases (p = 0.02). No significant difference in OS was observed between liver vs peritoneal oligometastatic disease (p = 0.29; median OS 9.2 vs 9.6 years).Treatment with surgery plus systemic therapy was associated with longer OS than systemic therapy alone (p = 0.015; median OS: 13.2 vs 6.1 years; HR: 2.699, 95% CI 1.210-6.016). Conclusions: In this study, subjects with oligometastatic GIST treated with surgery in addition to systemic therapy had longer OS than subjects treated with systemic therapy alone. This study highlights the need for prospective studies to assess treatment strategies for this patient population with a goal of creating a more standardized approach.