Clinical and pathological studies of borderline gastrointestinal stromal tumors

Background Borderline gastrointestinal stromal tumors (GISTs) are intermediate tumors between benign andmalignant variants;however,the clinical and pathological features of borderline GISTs remain poorly defined.This studyaimed to characterize GISTs and to identify a set of borderline criteria for practical use.Methods Medical records and specimens of 840 patients from 12 hospitals were retrospectively examined.Totally 485and 76 patients with any of the parameters predictive of either malignant or benign tumors were excluded.TheKaplan-Meier method was used to calculate disease-free survival and overall survival rates.Results Among the remaining 279 borderline GIST patients,223 were followed up for 1 to 31.48 years.Two patientsdeveloped local recurrence,and both were cured by subsequent operations alone.The 5-year disease-free survival andoverall survival rates were 99% and 100%,respectively.Morphologically,borderline GISTs typically exhibited moderatecellularity,and subsets of them also showed moderate atypia,low mitotic activities,or large tumor size.According to theNational Institutes of Health (NIH) consensus criteria,the risk levels of the 279 GISTs were classified to be very low tohigh.However,the disease-free survival rates were not significantly different among these risk groups (P=0.681).Conclusions The proposed borderline GIST criteria in the current study may complement the existing NIH criteria,based primarily on tumor size and mitotic count,in the evaluation of the biological behaviors of GISTs.Since a subset ofborderline GISTs with high risk level showed favorable outcome,the introduction of the borderline GIST system mayavoid overdiagnosis and over therapy.