Selective internal radioembolization (SIRT) allows to control liver metastases of gastrointestinal stromal tumors (GIST) failing treatment with tyrosine kinase inhibitors (TKI).

11540 Background: The liver and the peritoneum are the main area of metastatic spread in GIST. Liver resection does not play a role for hepatic metastases in comparison to f.e. colorectal cancer. If hepatic metastases are the only or major area of tumor progression and are resistant to available TKIs due to a missing mutation in KIT/PDGFRA/SDH (‘wildtype’) or after treatment with 1st/2nd/3rd/4th line therapy, interventional radioembolization with yttrium-90 (90Y) microspheres are promising treatment options, as radiation doses as high as 200Gy can be applied locally. We analyzed the long-term results of SIRT with respect to hepatic-progression-free survival (HEP-PFS) in a consecutive cohort of patients Methods: From 1/2008 to 1/2018, 2^6 pts (12f, 14m) with biopsy proven liver metastases of GIST which were the only (n = 13) or the dominant site of progression (n = 12) were treated by SIRT. Median age at GIST diagnosis had been 51.8 yrs and when receiving SIRT was 57.6yrs (range, 18–75yrs). The mutational status was ‘wildtype’ (n = 7, 2 NF-1), exon 11 (n = 7), exon 11+2nd mutation (n = 7), exon 9 (n = 3), exon 9+2ndmut (n = 1), and, exon 13 (n = 1). All patients except of two had prior TKI therapy: 1 line n = 3, 2 lines n = 11, 3-4 lines n = 9. Follow-up after SIRT was done via dynamic MRI and contrast-enhanced (CE)-CT, the median follow-up is 33.6 mos (range, 12-108mos) and all patients were followed until death Results:.The median hepatic-progression free survival (HEP-PFS) after SIRT was 17 months (range, 5-53+, 95%CI 10.7-23.8 mos). Of the patients with concomitant extrahepatic disease, the extraHEP-PFS was median 10 months. Twelve patients received next-line TKI therapy for progressive extrahepatic disease, whereas six patients required this for progressive liver metastases. When comparing the results according to the mutational status, patients with a ‘wildtype’ tumor showed a better median HEP-PFS of 19 mos (range, 12-53+, 95%CI 16.7-21.2 mos.) in comparison to KIT exon 9/11/13 mutated patients with only 14 months (range, 4-34 mos., 95%CI 6.5-21.4 mos), p < 0.11 (Wilcoxon). Conclusions: 90Y radioembolization (SIRT) offers a safe and effective treatment for patients with liver metastases of GISTs being the dominant site of tumor progression and with no drug treatment options available. In patients known to have no mutation in KIT/PDGFRA (wt, also NF-1 associated) it looks whether the results might be even more promising and SIRT could be used in earlier treatment lines.