Evaluation of Ki67 Index in Endoscopic Ultrasound-Guided Fine Needle Aspiration Samples for the Assessment of Malignancy Risk in Gastric Gastrointestinal Stromal Tumors

Abstract

<b><i>Background:</i></b> The risk of malignancy in resected gastrointestinal stromal tumors (GISTs) depends on tumor size, location, and mitotic index. Reportedly, the Ki67 index has a prognostic value in resected GISTs. We aimed to analyze the accuracy of endoscopic ultrasound (EUS)-guided fine needle aspiration (FNA) samples with reference to Ki67 index, using surgical specimens as the gold standard. <b><i>Methods:</i></b> Fifty-five patients who underwent EUS-FNA followed by surgical resection for gastric GISTs were retrospectively analyzed. Patients’ age and sex; tumors’ size and location; mitotic index, cell type, cellularity, pleomorphism, presence of ulceration, hemorrhage, necrosis, mucosal or serosal invasion, growth pattern, and Ki67 index based on pathology were investigated. <b><i>Results:</i></b> Location in fundus, ulceration, hemorrhage, mucosal invasion, and Ki67 index in surgical specimens were significant in predicting high-risk groups (<i>p</i> &#x3c; 0.05) on univariate analysis. Frequency of bleeding (<i>p</i> = 0.034) and the Ki67 index (<i>p</i> = 0.018) were the only independent significant factors in multivariate analysis. The optimal cutoff level of Ki67 was 5%, with 88.2% sensitivity and 52.8% specificity (<i>p</i> = 0.021). The mean Ki67 index was lower in EUS-FNA samples than in surgical specimens (2% [1–15] versus 10% [1–70], <i>p</i> = 0.001). The rank correlation coefficient value of Ki67 was 0.199 (<i>p</i> = 0.362) between EUS-FNA and surgical samples and showed no reliability for EUS-FNA samples. <b><i>Conclusion:</i></b> The Ki67 index in resected specimens correlated with high-risk GISTs, although it had no additive value to the current criteria. The Ki67 index in EUS-guided FNA samples is not a reliable marker of proliferation in GISTs.