Cytological Ki-67 in pancreatic endocrine tumors: a new "must"?

In the last decades, the incidence of neuroendocrine tumors (NETs) has been rising and this might be due to more awareness, improved diagnostic tools and a change in definition. The histopathological type of the tumor, its Ki-67 or MIB-1 proliferation index, size and location, as well as the age of the patient, seems to be the most important factor that affects prognosis and survival. In 2008, in one of our studies, we concluded that the cytological Ki-67 may improve the preoperative assessment of pancreatic NETs (pNETs), helping the clinician choosing the optimal therapeutical approach". Although the literature reports discordant opinions on the value of tumor proliferation markers in predicting a patient's prognosis, many studies have then reinforced the idea that Ki-67 expression in histological sections obtained from pNETs is an important predictor of their biological behaviour. The WHO classification of pNETs includes Ki-67 expression in the list of parameters (together with distant metastases, organ infiltration, dimension, angio/neuroinvasion, number of mitosis) determining the patient's prognosis. In conclusion we think that any study aimed to assess the correct biology and proliferative pattern of NETs contributes to the already known but still unclear attempt to define the correct individualized therapeutic strategy for each patient before surgery or any other therapeutic approach.