(P 174) INCIDENCE, TREATMENT PATTERNS, AND SURVIVAL OUTCOMES FOR ADULT PATIENTS WITH GASTROINTESTINAL STROMAL TUMOURS (GIST) IN ALBERTA, CANADA FROM 2008 - 2022.

Objective: GISTs represent approximately 1% of all gastrointestinal malignancies and are the most common mesenchymal tumour in the gastrointestinal tract. We aimed to better understand trends in incidence, treatment patterns and survival outcomes for patients with GIST in Western Canada.

Methods: Data from adult patients diagnosed with GIST in the province of Alberta, Canada (identified through a provincial registry) between 2008 and 2022 were extracted. Patient demographics, survival and treatment (surgery and systemic therapy) were collected. Descriptive statistics and Chi-Square goodness of fit tests were used to analyze demographic and incidence patterns of GIST over time. Overall survival outcomes were estimated using Kaplan-Meier analysis and Cox proportional hazards models. This study was approved by the Health Research Ethics Board of Alberta, Cancer Committee.

Results: A total of 693 cases of GIST were identified between 2008 and 2022 in Alberta, with a median follow up of 43.7 months. Table 1 lists baseline patient and tumour characteristics. The number of GIST diagnoses increased over time, with the highest incidence noted in 2020-2022 (p < 0.001). Most patients (n = 487, 70.3%) underwent surgery for their GIST, while 36.7% (n = 254) received systemic therapy with tyrosine kinase inhibitors. Systemic therapy was started prior to surgery in 50 patients, with treatment given for a median of 300 days before surgical intervention (range 86 – 560 days).

Median survival for patients with metastatic disease was 52.5 months, significantly less than patients with localized or locally advanced disease, in whom median survival was not reached (Figure 1, HR 6.78, 95% CI 3.56 – 12.90, p < 0.0001). Increasing age (HR 1.05, 95% CI 1.04 – 1.10, p < 0.001), and other/unknown primary location (HR 4.34, 95% CI 2.00 – 9.40, p = 0.018) were associated with poorer prognosis. Patient sex did not significantly affect prognosis in our cohort. Year of diagnosis (Figure 2) was also not associated with survival outcomes.

Compared to patients treated with systemic therapy after surgery, patients treated with surgery alone (HR 1.95, 95% CI 1.13 – 3.40, p = 0.016), systemic therapy alone (HR 2.91, 95% CI 1.71 – 4.90, p < 0.001) and no treatment (HR 3.97, 95% CI 2.32 – 6.80, p < 0.001) had worse survival outcomes. There was no statistically significant difference between patients treated with systemic therapy prior to surgery as compared to after surgery (HR 1.52, 95% CI 0.71 – 3.20, p = 0.27).

Conclusion: The rate of GIST diagnosis increased in Alberta between 2008 and 2022. Further studies are needed to determine whether this pattern also exists in other jurisdictions, and to identify potential causes for this increase. Additional data analyses assessing mitotic rate, molecular pathology and GIST risk stratification in our cohort are ongoing. We observed similar survival outcomes in our cohort over time, and similar outcomes with systemic therapy used before or after surgery. However, future studies are planned to assess the impact of the changing systemic and locoregional therapy landscape for patients with metastatic disease. Our data highlight the importance and value of multidisciplinary management of GIST patients, as patients in our cohort with localized or locally advanced disease treated with systemic and surgical therapy had excellent long-term outcomes.