Development of a prognostic prediction model for tumor recurrence or progression in gastrointestinal stromal tumors: integrating inflammatory blood indices with 5 mm2 versus 50 high-power field mitotic counts.

backgroundThe behavior of gastrointestinal stromal tumors varies according to tumor size, location, mitotic rate, and rupture. Traditional mitotic counting in 50 high-power fields (HPF; 5.3 mm2) may overestimate progression risk, as 5 mm2 corresponds to 20-25 HPF under modern microscopy. However, the 50-HPF method remains widely used. This study evaluated the impact of two mitotic counting methods on risk classification and developed a prognostic model combining inflammatory biomarkers with clinicopathological factors.

methodsWe retrospectively analyzed 150 patients who underwent resection at Songklanagarind Hospital between 2009 and 2021. Patients who had received neoadjuvant therapy or had a second primary cancer were excluded. Mitosis was evaluated using both methods. Clinicopathological and serum biomarker data were collected. The primary outcome was 5-year disease-free or progression-free survival. The model was developed using forward stepwise variable selection based on the time-dependent area under the curve and internally validated by bootstrapping.

resultsThe 50-HPF method overestimated the Armed Forces Institute of Pathology classification in 14.2% of cases. A model incorporating tumor size, location, rupture, mitotic count within 5 mm2, and systemic immune-inflammation index achieved the highest area under the curve of 0.939 in both training and validation sets, outperforming previous models. The 5-mm2 method demonstrated superior performance to the 50-HPF method across all models (0.939 vs. 0.919 for the proposed model).

conclusionsMitotic counting in 50 HPF overestimated risk classification in certain cases. Incorporating systemic immune-inflammation index and using a 5 mm2 mitotic count enhanced prognostic model performance.