Impact of neoadjuvant imatinib duration and tumor response on recurrence-free survival in locally advanced gastrointestinal stromal tumors: a retrospective multicenter cohort study

BACKGROUND: Neoadjuvant imatinib (IM) is widely used in locally advanced gastrointestinal stromal tumors (GISTs) to improve resectability and reduce recurrence, but optimal duration and the prognostic role of tumor response remain unclear. METHODS: We performed a multicenter retrospective cohort study of patients with locally advanced GISTs who received preoperative imatinib and surgery between 2014 and 2024 at four tertiary centers in China. Tumor response was assessed by Response Evaluation Criteria in Solid Tumors (RECIST) 1.1, and a novel parameter, the Percent Tumor Response Index (PTRI), was proposed to integrate baseline size with shrinkage rate. Recurrence-free survival (RFS) and overall survival (OS) were analyzed by Kaplan–Meier and Cox regression. RESULTS: Among 168 patients (median treatment 7.5 months), all achieved disease control: partial response (PR) in 52.4% and stable disease (SD) in 47.6%. Median tumor size decreased from 10.0 to 7.0 cm (p < 0.001). After a median follow-up of 53 months, 3- and 5-year RFS rates were 88.6% and 83.2%, and OS rates were 97.6% and 92.0%. Using maximally selected rank statistics (MSRS), 8 months was identified as a potentially meaningful threshold. Patients treated ≤ 8 months had superior RFS compared with > 8 months. In multivariable Cox regression analysis, a preoperative imatinib duration exceeding 8 months (HR 2.40, p = 0.034) and a postoperative mitotic count > 5/5 HPF (HR 2.31, p = 0.042) were independently associated with worse RFS, whereas a higher Percent Tumor Response Index (PTRI), a newly proposed exploratory metric, was associated with a reduced risk of recurrence, corresponding to a 32% risk reduction per unit increase (p = 0.002). CONCLUSIONS: In our cohort, a preoperative imatinib duration exceeding 8 months for locally advanced GISTs was associated with inferior RFS. Elevated PTRI predicted favorable recurrence outcomes, whereas higher postoperative mitotic count indicated poorer prognosis.