Current ESGE guidance advises early gastroscopy within a few months of diagnosis for small subepithelial lesions, followed by periodic long-term surveillance with shorter intervals for larger lesions. These recommendations are based on low-quality evidence, and the true growth behavior of GISTs remains uncertain. Our 10-year review of EUS-detected gastric and duodenal GIST aims to assess growth patterns and evaluate whether current surveillance intervals are justified or could be safely extended. 

A retrospective study was conducted at a district general hospital, reviewing EUS examinations of endoscopically or biopsy-confirmed gastric and duodenal GISTs between January 2015 and October 2025. For patients with at least one qualifying EUS, any prior EUS before 2015 was included to preserve surveillance continuity. Data collected includes lesion size, location, EUS intervals, biopsy status, and management plan. Lesions were grouped by baseline size (≤10 mm, >10–15 mm, >15–20 mm, and >20 mm). Growth was defined as an increase of ≥5 mm or ≥20% in maximal diameter between first and last EUS. Event rates per person-year were calculated to estimate growth incidence, with 95% confidence intervals (CI) derived using binomial or Poisson methods. 

A total of 105 patients (274 EUS procedures) were reviewed and categorized by initial GIST size. 

For lesions ≤10 mm, 11 of 17 patients underwent more than one EUS, representing 32.8 person-years. No growth events were recorded (0/11; 0%, 95% CI 0–27.3%). The event rate per person-year was therefore 0 (upper 95% bound = 0.0915 per person-year). Using this upper confidence limit to model the worst plausible scenario, the theoretical cumulative probability of growth was estimated at ≤24% over 3 years and ≤31% over 4 years. These values represent the statistical ceiling implied by zero events, not observed risk. In practice, all ≤10 mm lesions remained entirely stable. 

For lesions >10–15 mm, 12 of 32 patients had serial follow-up representing 40.8 person-years. One lesion (1/12; 8.3%, 95% CI 0.2–38.5%) enlarged from 15 mm to 30 mm after 24 months, yielding an event rate of 0.0246 per person-year (95% CI 0.0006–0.136). The modeled upper 95% cumulative risk was 7.23% at 3 years and 9.52% at 4 years. Although the upper cumulative risk is numerically smaller than that for the ≤10 mm group, this reflects narrower statistical uncertainty from one observed event; the true growth probability in ≤10 mm lesions is lower, but its confidence interval is wide due to the absence of events. 

In the >15–20 mm category, 9/22 patients had serial EUS (25.2 person-years). 3 patients had growth events (3/9; 33.3%, 95 % CI 7.5–70.1%), giving an event rate of 0.119 per person-year (95% CI 0.025–0.347), corresponding to an upper 95% cumulative risk of about 30% at 3 years and 40% at 4 years. 

Among lesions >20 mm, 11 of 50 patients had serial EUS (35.2 person-years). 8 patients had growth events (8/11; 72.7%, 95% CI 43–90%). The event rate was 0.228 per person-year (95% CI 0.098–0.450), equivalent to an upper 95 % cumulative growth risk of 74.08% at 3 years and 83.47% at 4 years. 

This review demonstrates that GISTs ≤10 mm show no measurable growth. Although Poisson modeling allows a theoretical 31% risk at 4 years, this reflects statistical uncertainty rather than clinical risk. The absence of any true growth events supports extending surveillance for ≤10 mm GISTs every 3–4 years. For 10–15 mm lesions, a single event over 40 person-years corresponds to a modeled cumulative risk of 9.52% at 4 years, making the current ESGE recommendation justified. Lesions >15 mm showed substantially higher event rates, confirming that shorter surveillance remains appropriate for this subgroup.