Utilization of Mutational Analysis (MA) in Gastrointestinal Stromal Tumor (GIST) Management in British Columbia (BC) Between January 2008 to December 2017: a Retrospective Population-Based Study

Purpose To examine oncologists' practice pattern of ordering MA in localized and metastatic GISTs in British Columbia (BC). Methods Patients diagnosed with GIST from January 2008 to December 2017 in BC were identified. Chart review was performed to determine clinical characteristics and the use of MA as part of their oncologic care. Results The cohort included 411 patients: median age 64 (18-94 years), 49.1% male, primary site included stomach (53%), small intestine (32%), and others (15%). Sixty-nine percent had localized disease, while 13% presented with de novo metastatic disease and 18% had recurrent metastatic disease. MA was ordered in 41% of the patients overall, 28% in localized, and 70% in metastatic settings (63% in de novo metastasis and 78% in recurrent metastasis). Among patients with localized disease, higher MA use rates were observed among those undergoing neoadjuvant/adjuvant treatment (45%) compared to those not receiving systemic therapy (18%). While MA use rates in localized GIST did not change over time (28.5% before 2015 and 28% after 2015), MA use in metastatic disease increased from 54% before 2015 to 79% after 2015. Among all MA ordered for metastatic disease, 82.4% were ordered at the time of de novo metastatic diagnosis, and 77.4% were ordered either at the time of recurrent metastatic diagnosis or earlier when the disease was localized. Conclusion MA use has remained stable for localized disease but has increased after 2015 in the metastatic setting which may be due to evolving sequencing technology, expansion of metastatic treatment options, and enhanced awareness of MA.