Atypical Pituitary Adenoma: A Clinicopathologic Case Series

Background: In 2004 the World Health Organization (WHO) classified atypical pituitary adenoma as a distinct adenoma subtype. However, the clinical significance of this distinction remains undetermined.

Objective: We sought to better characterize patient characteristics, tumor features, and treatment outcomes associated with atypical pituitary adenoma.

Methods: We retrospectively reviewed the records of patients undergoing evaluation at the University of California, San Francisco (UCSF). From 2010–14, 34 tumors demonstrated elevated mitotic index, positive p53 staining, and K_i-67 proliferative index >3%, and were included in our study. Log-rank, Kaplan-Meier, and Fisher’s exact test were used for statistical analyses.

Results: There were 21 female patients (62%) and 13 male patients (38%), ranging in age from 10 to 65 years with a median tumor size of 2.5 cm. The majority of tumors (65%) demonstrated local invasion, a feature more often associated with macroadenomas (Fisher’s exact test, p = 0.003). There was a trend toward significance when analyzing gender and tumor size; female patients appeared to present with larger tumors (Fisher’s exact test, p = 0.132). Five patients (15%) suffered tumor recurrence, at a median time of 5 years. We found no statistically significant association between hormone positivity, size, extent of resection, invasion, and recurrence.

Conclusion: Clinical distinction between typical and atypical adenoma remains elusive. Our analyses suggest that atypical adenomas may tend to be hormonally positive, more invasive as they get larger, exhibit a female preponderance, with a statistical trend toward women presenting more frequently than men with macroadenomas. Factors associated with recurrence remain unclear.