Supplementary Material for: Molecular Profile of Gastrointestinal Stromal Tumors in Sixty-Eight Patients from a Single Swiss Institution

<b><i>Introduction:</i></b> Gastrointestinal stromal tumor (GIST) is the most common mesenchymal neoplasm of the gastrointestinal tract. It has distinct molecular features and primarily affects the <i>KIT</i> and <i>PDGFRA</i> genes. <b><i>Objective:</i></b> We wanted to assess the molecular profile of 68 GIST patients who were sequenced consecutively between 2014 and 2019 at our institute of pathology. <b><i>Methods:</i></b> Our cohort comprised 60 primary and 8 metastatic GIST patients; 43 and 57% of the cases, respectively, were analyzed by Sanger sequencing or next-generation sequencing (NGS). <b><i>Results:</i></b> Of the 60 primary GIST patients, 47 (78%) showed a <i>KIT</i> mutation; 2 cases showed a double <i>KIT</i> mutation, and 1 of these was a therapy-naive GIST. Nine (15%) patients harbored a <i>PDGFRA</i> mutation, 2 (3%) had a <i>BRAF</i> mutation, 1 (2%) had a <i>PIK3CA</i> mutation, and 1 (2%) did not show any mutation. One <i>BRAF</i> and the <i>PIK3CA</i> mutation have not been described in GIST before. All metastatic GIST harbored exclusively <i>KIT</i> mutations. <b><i>Conclusion:</i></b> A retrospective analysis of GIST sequenced at our institute revealed incidences of <i>KIT</i> and <i>PDGFRA</i> mutations comparable to those in other cohorts from Europe. Interestingly, we found 2 previously undescribed mutations in the <i>BRAF</i> and <i>PIK3CA</i> genes as well as 1 treatment-naive case with a double <i>KIT</i> mutation in exon 11.