Evaluation of the potential of the Ki67 index to predict tumor evolution in patients with pituitary adenoma

The aggressive course of a number of pituitary adenomas requires the investigation of potential predictors. This study aimed to investigate the proliferation marker Ki67 as a predictor of postoperative outcome in patients with pituitary adenoma regarding recurrence and regrowth of the tumor, using a Ki67 cut-off value of 3%. This retrospective study included 52 patients with pituitary adenoma who had undergone adenomectomy and had a pituitary image taken at least 1 year after surgery. Patients were divided according to Ki67 expression into high (≥3%) vs. low (<3%) levels of Ki67. The two groups were similar regarding the preoperative tumor invasion grade. The Ki67 index ranged from 0 to 30%; in 23 cases, Ki67 was ≥3%. The two groups were similar regarding tumor recurrence and regrowth: 4 cases (28%) of recurrence in the Ki67<3% group vs. none in the Ki67≥3% group (P=0.26); and 2 cases (13%) of regrowth in the Ki67<3% group vs. 7 cases (43%) in the Ki67≥3% group (P=0.11). A subgroup analysis was performed for nonfunctioning adenomas. Recurrence rates remained similar between groups (Ki67<3% group: 1 case [20%]; Ki67≥3% group: none; P>0.99), whereas regrowth rates were higher in the Ki67≥3% group (6 cases [67%] vs. 2 cases [17%] in the Ki67<3% group; P=0.03). The patient with the highest Ki67 index (30%) developed pituitary carcinoma. The results allow us to suggest the adoption of a stricter control of image monitoring in nonfunctioning adenomas with incomplete resection associated with a Ki67 index ≥3%.