MKI67 and gastrointestinal stromal tumor: It is considered a proliferation-related nuclear marker of tumor cells.[16] The mitotic index reflects the M stage of mitosis only; however, as the Ki67 can recognize most of the proliferating cells except for G0, it is considered to be more appropriate as an marker of the malignancy of GIST.[17] To date, a number of studies have reported a correlation between Ki67 expression and malignant risk of GIST.[18–20] However, because of conflicting results and limited sample size, the significance of Ki67 in predicting risk of malignancy with GIST is still in dispute.