163P Gastrointestinal stromal tumours (GIST) in adolescents and young adults (AYA) in an Asian institution from 2002 to 2018

Abstract

GIST is not common in AYA patients and the data on AYA GISTs are limited. In our institution, the typical adult GIST patient is male (52.9%), with mutations in KIT (53.6%) or PDGFR (4.2%), has gastric as the primary location (54.4%), and a five-year overall survival (OS) of 51%. We studied the clinical and genetic characteristics and prognoses of AYA GISTs. All GIST patients diagnosed between the ages of 16-39 at National Cancer Centre Singapore from 1 January 2002 to 31 December 2018 were included. We retrospectively studied their clinico-molecular characteristics and outcomes. 41 AYA GIST patients were seen with a median age of 34 years old. 25 patients (61.0%) were male. 27 patients (65.9%) were Chinese. 9 (22.0%) had metastatic disease at diagnosis. The tumours were primarily in the jejunum/ileum (41.5%, n=17) or stomach (34.1%, n=14). 25 patients (61.0%) had tumor mutation testing performed. Of these, 19 (76%) had KIT and one (4%) had PDFGRA. 5 (20%) were KIT/PDGFR wildtype. Of those with KIT mutations, 17 (89.5%) were in exon 11, while 2 (10.5%) were in exon 9. The PDGFRA mutation was in exon 18. No data is available on genetic syndromes. 24 patients (58.4%) received curative-intent treatment with 3 (12.5%) subsequently had local recurrences. 14 (58.3%) received imatinib in a neoadjuvant/adjuvant setting. 17 patients (41.5%) received palliative-intent treatment with 13 (76.4%) receiving palliative imatinib. 9 (52.9%) had Sunitinib after progression. The median follow-up was 48 months (0-165). 6 patients (14.6%) had demised. Median OS for all patients was 162.0 months (95% CI: 80.8– 243.2) with no significant differences with regards to age (p=0.07), gender (p=0.91), presence of a sensitising mutation (KIT Exon 9 and 11) (p=0.26), and treatment intent (p=0.2). A significant OS difference was found between patients undergoing curative or palliative intent (162.0 vs 65.0 months, p=0.001) and in patients with different primary tumor location (p=0.029). Out of the 6 patients with uncommon primary tumor locations, 3 had demised. AYA GISTs differ from adult GIST. In our series, 61.0% had tumor mutation analysis performed. AYA GIST also has a higher rate of small intestine primary. Further studies are needed to evaluate the low mutation and genetic testing and clinico-molecular differences to better understand how these affect outcomes.