MKI67 and neuroendocrine neoplasm: Using evidence from 8 studies, for a total of 268 NEC affected patients, the systematic review showed that NECs with a low Ki67 LI had a better prognosis than the subgroup with higher Ki67 LI but worse than G3 neuroendocrine tumors suggesting that NECs are a heterogeneous disease for the pathology findings, the clinical behavior and the treatment response.