TP53 and pituitary gland adenoma: In 2007, the World Health Organization defined atypical pituitary adenomas as those with a Ki-67 expression >3%, excessive p53 expression and increased mitotic activity.3 Chiloiro et al23 have reported that pituitary adenomas with a Ki-67 expression ≥1.5% had a higher risk of recurrence and shorter disease-free survival compared with those with a Ki-67 expression <1.5%.