Role of Ki-67 Proliferation Index in the Assessment of Patients with Neuroendocrine Neoplasias Regarding the Stage of Disease

Neuroendocrine neoplasias (NEN) of the gastroenteropancreatic (GEP) system frequently present with metastatic deposits. The proliferation marker Ki-67 is used for diagnosis and to assess the prognosis of disease. The aim of our study was to evaluate the usefulness of Ki-67 % in the assessment of NEN patients with regard to their disease stage in clinical practice. Additionally, a comparative analysis of Ki-67 levels among different sites of disease was performed. This retrospective study included patients with GEP NEN referred to our center from 2010 to 2012. The NEN diagnosis was confirmed by standard histopathology. Ki-67 immunohistochemistry was done on paraffin-embedded sections using an automated Leica immunohistochemistry machine. NEN grading was carried out according to European Neuroendocrine Tumor Society recommendations (low grade [G1] to intermediate grade [G2], well to moderately differentiated neuroendocrine neoplasms; high-grade [G3], moderately to poorly differentiated neuroendocrine neoplasms). Results of tumor staging and grading were correlated. In a subgroup of cases, comparative analysis of Ki-67 levels in different sites of disease was carried out. One hundred sixty-one GEP NEN patients were included in the study. Metastatic disease was seen in 46.1 % (53/115) of G1 tumors, 77.8 % (28/36) of G2 tumors, and 100 % of (10/10) G3 tumors (p = 0.0002). When stratified according to primary tumor site, metastatic disease was documented in 42.9 % (36/84) of patients with pancreatic NEN and in 91.9 % (34/37) of those with small intestinal primary. Stage IV metastatic disease was present in 27.8 % (32/115) and 72.2 % (26/36) of the G1 and G2 tumors, respectively, and in 90 % (9/10) of the G3 tumors. Assessment of the Ki-67 index for a subset of cases at metastatic sites as well as the primary tumor site showed discrepancies in 35.3 % cases. In 7/9 (77.8 %) patients with liver metastases, Ki-67 % was higher in the liver lesions than in the primary tumor. Patients with GEP NEN exhibiting a high Ki-67 proliferation index present with metastatic disease in the vast majority of cases. Depending upon the primary tumor site, metastases are to be expected also in tumors with low Ki-67 %, although they are considered less aggressive. Different disease sites may express heterogeneous Ki-67 levels.