Characterizing gastrointestinal stromal tumors and evaluating neoadjuvant imatinib by sequencing of endoscopic ultrasound-biopsies

AIM: To evaluate endoscopic ultrasound (EUS)-guided biopsies for the pretreatment characterization of gastrointestinal stromal tumors (GIST) to personalize the management of patients. METHODS: All patients with lesions suspected to be GIST who were referred for EUS-sampling at a tertiary Swedish center were eligible for inclusion 2006-2015. During the observational study phase (2006-2011), routine fine-needle-aspiration (EUS-FNA) was performed. In 2012-2015, we converted to an interventional, randomized protocol with dual sampling EUS-FNA and fine-needle-biopsy-sampling (EUS-FNB) for all lesions. c-KIT- and DOG-1-immunostaining was attempted in all samples and a manual count of the Ki-67-index was performed. FNB-sampled tissue and the resected specimens were subjected to Sanger sequencing of the KIT and platelet-derived growth factor alpha (PDGFRA) genes. RESULTS: In all, 64 unique patients with GIST were included, and of these, 38 were subjected to pretreatment dual sampling. EUS-FNB had a higher diagnostic sensitivity when compared head-to-head with EUS-FNA (98% vs 58%, P < 0.001) and was more adequate for Ki-67-indexing (Ki-67(EUS)) (92% vs 40%, P < 0.001). Sequencing of EUS-biopsies was successful in 43/44 (98%) patients, and the mutation profiles (KIT-mutation 73%, PDGFRA-mutation 18%, wild-type 7%) were fully congruent with those detected in the corresponding resected specimens. In imatinib-naïve patients, the Ki-67(EUS) was comparable with the Ki-67-index in the corresponding surgical specimens (Ki-67(SURG)) (2.7% vs 2.9%, P = 0.68). In patients treated with neoadjuvant imatinib who also carried mutations indicating sensitivity, the Ki-67(EUS) was higher than the Ki-67(SURG) (2.5% vs 0.2%, P = 0.005), with a significant reduction in the Ki-67-index of -91.5% (95%CI: -82.4 to -96.0, P = 0.005). CONCLUSION: EUS-guided biopsy sampling is accurate for the pretreatment diagnosis and characterization of GISTs and allows the prediction and evaluation of tumor response to neoadjuvant imatinib therapy.