Abstract 54P
Background
Gastrointestinal stromal tumour, GIST, is the most common intra-abdominal sarcoma and can occur throughout the gastrointestinal tract but most often in the stomach or small intestine. The treatment is surgical resection, sometimes combined with an adjuvant tyrosine kinase inhibitor. Neoadjuvant treatment with imatinib is indicated for large tumours and to minimize postoperative morbidity. The effect of the neoadjuvant treatment depends on the sensitivity of the tumour-driving mutation to imatinib. It is evaluated structurally with a computed tomography scan or metabolically with FDG-PET. We have investigated the clinical utility of FDG-PET in the neoadjuvant treatment setting of GIST at Sahlgrenska University Hospital in Gothenburg, Sweden.
Methods
We identified patients diagnosed with GIST between 2002 and 2020 who received pretreatment with imatinib at Sahlgrenska University Hospital. The response was assessed based on the FDG-PET examinations and compared with the mutational analysis.
Results
Of 125 patients who received neoadjuvant imatinib, 69 had at least one PET scan. Mutation analysis was missing in 19 patients, so the patient cohort consisted of 51 patients. Tumours with mutations sensitive to imatinib showed a response to PET in 87% (n=34) of patients with an odds ratio of 4.86 (p=0.037). In cases where the sensitivity of the tumour mutation to imatinib was uncertain, reduced FDG uptake at PET occurred in 58% (n=7) of the patients.
Conclusions
The PET examination was often challenging to interpret. It contributed to managing patients without FDG-PET response and with an uncertain imatinib-sensitive tumour mutation. Evaluation of neoadjuvant treatment with FDG-PET was unnecessary in patients with imatinib-sensitive tumour mutation.
Clinical trial identification
Editorial acknowledgement
Legal entity responsible for the study
Stefan Lindskog.
Funding
Gothenburg University.
Disclosure
All authors have declared no conflicts of interest.