Grade 2 pancreatic neuroendocrine tumors: overbroad scope of Ki-67 index according to MRI features
To evaluate the value of MR imaging features in stratifying Grade 2 (G2) pancreatic neuroendocrine tumors (PNETs) using the 5% cut-off value of the Ki-67 index as reference standards.
Materials and methods
Between January 2010 and October 2016, 41 G2 PNET patients (One patient had 3 tumors) with preoperative MR imaging were included. Tumor grading was based on the revised 2016 World Health Organization classification of PNETs. MR imaging features included size, shape, consistency, T1-w and T2-w signal intensities, enhancement pattern, apparent diffusion coefficient (ADC) ratios (tumor/normal pancreatic parenchyma).
16 Ki-67 index < 5% tumors (SKIT, 37.2%) and 27 Ki-67 index ≥ 5% tumors (LKIT, 62.8%) of G2 were evaluated. The LKIT showed solid consistency (85% vs. 50%, P < 0.05), incomplete envelope-like reinforcement in a delayed phase (74% vs. 62%, P < 0.05), and liver or lymph node metastases (67% vs. 31%, P < 0.05) more frequently than did SKIT. However, ADC ratios of LKIT were smaller than SKIT (0.85 ± 0.23 vs. 1.29 ± 0.39, P = 0.001). Using binary logistic regression analysis, the ADC ratio was an independent significant differentiator of SKIT from LKIT. The AUROC of ADC ratios was 0.816 ± 0.07. The optimal cut-off value for the identification of LKIT was 1.25 × 10−3 (sensitivity 96.3%, specificity 62.5%).
MRI features may identify the overbroad scope of G2 PNETs and help predict Ki-67 values, as a surrogate for tumor aggressiveness, in G2 PNETs. An optimal cut-off value for predicting Ki-67 status (≥/< 5%) was 1.25 × 10−3 of ADC ratio.
KeywordsPancreas Neuroendocrine tumors Diffusion magnetic resonance imaging Ki-67 antigen Neoplasm grading
The authors state that this work has not received any grants. M.S. Zeng would like to declare that the whole article was original research that has not been published previously, and not under consideration for publication elsewhere.
Compliance with ethical standards
Conflict of interest
Author Yabin Hu declares that he has no conflict of interest. Author Shengxiang Rao declares that he has no conflict of interest. Author Xiaolin Xu declares that she has no conflict of interest. Author Yibo Tang declares that she has no conflict of interest. Author Mengsu Zeng declares that he has no conflict of interest.
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
As this is a retrospective study, informed consent from the patients was not required.