Clinical impact of primary and secondary KIT mutations on the efficacy of molecular-targeted therapies in gastrointestinal stromal tumors.

Background: Gastrointestinal stromal tumors (GISTs) are commonly driven by primary mutations in KIT or PDGFRA. Imatinib is the first-line therapy for GISTs. However, secondary mutations frequently emerge during imatinib treatment, contributing to resistance and influencing the efficacy of subsequent tyrosine kinase inhibitors, such as sunitinib and regorafenib. This study aimed to investigate the clinical relevance of both primary and secondary KIT mutations in treating and prognosing unresectable or recurrent GISTs.

Methods: Ninety patients with unresectable or recurrent GISTs treated at our institution between 2000 and 2017 were retrospectively analyzed. Genetic testing was performed before the initial drug administration to guide first-line imatinib therapy based on the primary mutation profile. In 64 imatinib-resistant patients, additional genetic testing was conducted on tissues obtained from resistant lesions. Treatment response and prognosis were compared across mutational profiles.

Results: The most common primary mutation was KIT exon 11 (76.7%), followed by exon 9 (12.2%). Patients with exon 9 mutations showed superior progression-free survival with sunitinib than those with exon 11 mutations. Among patients with exon 11 primary mutations, secondary mutations were identified in 79.2%, predominantly in KIT exon 13/14 (47.9%) or 17/18 (31.3%). Sunitinib was more effective in patients with secondary exon 13/14 mutations, whereas regorafenib was significantly more effective in those with exon 17/18 mutations.

Conclusions: Secondary KIT mutations play a crucial role in imatinib resistance and the efficacy of second- and third-line therapies. Genetic profiling at the initial diagnosis and at the time of resistance may provide more personalized and effective treatment strategies.