MKI67 and neoplasm: In our previous studies, the most important characteristics of refractory PAs include refractoriness to standard therapies, including surgery, radiotherapy and conventional medical treatment; tumor infiltration of the adjacent structures based on either radiological images or intraoperative findings; a cut-off value of > 3% for Ki-67; increasing TGR > 2% per month; and tumor recurrence within 6 months after surgery (7, 8).