Association Between the Ki-67 Index, Tumor Size and Postoperative Structural Persistence in Non-functioning Pituitary Neuroendocrine Tumors: A Single-Center Experience

Introduction Non-functioning pituitary neuroendocrine tumors (NF-PitNETs) represent more than half of pituitary neoplasms. Features linked to greater aggressiveness include adrenocorticotropic hormone immunopositivity, plurihormonal or null-cell phenotype, elevated Ki-67 index (≥3%), and size ≥40 mm. However, evidence remains inconsistent, underscoring the need for further investigation into their biological behavior. Methods A retrospective study of medical records of patients with diagnoses related to pituitary pathology from 2010 to 2020 was conducted. The primary objective of this study was to evaluate the association between the Ki-67 proliferation index and tumor size with post-surgical structural persistence in patients with NF-PitNETs. The sample consisted of 81 patients who met the inclusion criteria. Clinical and paraclinical characteristics were recorded. The data were analyzed using univariate description and bivariate analysis, applying Fisher's test for the outcome of post-surgical structural persistence. Results The prevalence of NF-PitNETs was 58%. The most frequent symptoms were visual field disorders in 70%, followed by headache in 66%. Regarding structural persistence, a statistical association was found between the presence of Ki-67 ≥ 3% (p-value: 0.028) and tumor size ≥ 40 mm (p-value: 0.030). Conclusion The prevalence of NF-PitNETs is high, and the preoperative variable of tumor size (≥ 40 mm) and the Ki-67% index ≥ 3% reported in postoperative pathology were associated with greater structural persistence.