A novel risk score after neoadjuvant imatinib predicts relapse-free survival in patients with gastrointestinal stromal tumours (GIST).

IntroductionSurgery remains the cornerstone of management of localized GIST. Neoadjuvant imatinib facilitates surgery and allows in vivo monitoring of tumour response to therapy. There are no predictive tools to guide the duration of treatment. This study evaluates the impact of clinical and pathological variables on relapse-free survival (RFS) after neoadjuvant imatinib.Material and methodsSingle-centre retrospective study of 90 GIST patients who underwent radical surgery after neoadjuvant imatinib. Univariate and multivariate Cox regression analyses were performed to determine the association of clinicopathological variables to RFS. Evaluate Cut-points were used to identify values associated with significantly different outcomes. Between-group differences were assessed with the use of the stratified log-rank test.ResultsUnivariate Cox regression analyses showed a significant association of RFS with initial tumour size (ITS) (HR 1.11, p = 0.002), maximal tumour shrinkage (MTS) (HR 11.7, p = 0.023) and residual mitotic count (RMC) (HR 1.09, p ≪ 0.001). These results were confirmed in a multivariate model (ITS, p = 0.001; MTS, p = 0.003; RMC, p ≪ 0.001). Cut-points for ITS, MTS and RMC were established at 9.8 cm, 41 % reduction in size and 2 mitoses, respectively. Patients with large tumours ≥9.8 cm, ≤41 % reduction in size and ≥2 mitoses had shorter RFS. A combined score of these three variables allowed for accurate classification into two risk categories (p ≪< 0.001): low (0 or 1 factor) and high-risk (2 or 3 factors). Post-operative imatinib did not influence survival outcomes in either low -risk (HR 1.2, p = 0.83) or high-risk patients (HR 1.6, p = 0.35).DiscussionITS, MTS and RMC are associated with shorter RFS in patients with localized GIST treated with neoadjuvant imatinib. If validated, these findings could guide the design of prospective studies that de-escalate or intensify adjuvant treatment.