(P 300) GASTROINTESTINAL STROMAL TUMORS (GIST) IN YOUNG ADULTS (YA): A BRAZILIAN COHORT OF PATIENTS

Objective: The literature on clinical and biological GIST characteristics in YA patients (18 – 40 years at diagnosis) is scarce. This retrospective cohort study aims to describe the clinical, pathological, and molecular characteristics of GIST in YA patients, comparing findings with a group of older adults (OA) with GIST.

Methods: All GIST patients diagnosed between January 2010 and December 2023 who received first treatment at A.C.Camargo Cancer Center (Sao Paulo, Brazil) were included. Patients whose diagnosis was not confirmed by one of our sarcoma expert pathologists were excluded. GIST risk was determined by the modified NIH criteria. Overall survival (OS) was estimated using Kaplan-Meier method. Comparison between YA and OA (> 40 years at diagnosis) groups were performed by Chi-square, Fisher’s exact, Mann-Whitney U test.

Results: From 402 GIST patients treated in our center, 249 were included in this study: 18 YA (7.2%) and 231 OA (92.7%). In the YA cohort, 12 (66.7%) were female, median age 34 years. Main primary tumor locations for YA patients were stomach (44.4%) and small intestine (24.5%), and median tumor size was 5.4 cm (2 – 17.1 cm). Most of the YA patients had disease symptoms at diagnosis (72.2%). Four (22%) YA with localized disease presented high-risk GIST, and 6 (33%) YA patients had metastatic disease at diagnosis, most of them (3 patients) presenting metastasis to the liver. One YA patient had a known genetic predisposition which was a germline SDHA mutation, and another one harbored a germline MUTYH pathogenic mutation. GIST genetic profile test was performed for 51 patients (20.5%): 11 YA patients (61%) and 40 OA (17%). In the YA group, a KIT exon 11 mutation was found in 7 patients, a PDGFRA D842V mutation in 3 patients, and a SDHA mutation in 1 patient. The characteristics of the entire cohort are presented in table 1. No significant differences were found between the two subgroups regarding gender, location, size, morphology, risk classification, and mutation status. YA patients presented significantly more metastatic disease at diagnosis compared to OA (33.3% versus 11.7%, respectively; p = 0.02). With a median follow-up of 48 months (95% CI 37 – 59 months), median OS for all patients was not reached (95% CI 135 – 151 months). No death in the YA group was reported. Five-year OS rate was 92.2% and 100% in the OA and YA groups, respectively.

Conclusion: GIST presenting in the YA population is rare and cannot be considered completely similar to the typical OA GIST. In our series, we found a high percentage of small intestine GIST and high-risk tumors in the YA patients. Although they presented more metastatic disease at diagnosis, the survival was good. In addition, our findings show that, at the time of diagnosis, physicians were more prone to order genetic GIST testing for the YA than for the OA patients.