MKI67 and pituitary gland adenoma: In 2016, a novel concept of “refractory pituitary adenoma” was raised by Dai et al. [18], which is defined as follows: (1) tumor infiltrates adjacent structures according to imaging and surgical findings, (2) the Ki-67 index is over 3% and growth velocity is more than 2% per month, (3) current treatments fail to control tumor growth and/or hormonal hypersecretion, (4) tumor recurrence occurs within 6 months after surgery.