Aggressive Pituitary Adenoma Not Fulfilling the New High-Risk Criteria with Progression after 18-Year Stable Clinical Course: Case Report

Background: The World Health Organization (WHO) classification of tumors of the endocrine organs was revised in 2017. The term atypical adenoma is no longer recommended, and tumors with rapid growth, radiologic invasion, and high K i-67 labeling index are defined as high-risk adenomas. In this article, we present the case of an aggressive pituitary adenoma not fulfilling the new high-risk criteria with extraordinary rapid progression after very long stable disease, and discuss the remaining problem of the new criteria in terms of a complicated balance between pathologic findings and clinical features. Case Description: A 67-year-old man was admitted with sellar tumor. Serum prolactin concentration was high at 4,552.2 ng/mL. Transsphenoidal surgery achieved subtotal removal. Histologic diagnosis was lactotroph cell adenoma, and K i-67 labeling index was 2.6%. Postoperatively, magnetic resonance imaging revealed no evidence of tumor regrowth, but terguride or cabergoline administration was continued for slight hyperprolactinemia. Second surgery was performed 18 years after initial surgery because the tumor showed extraordinary rapid regrowth and hyperprolactinemia of 969 ng/mL. Histologic diagnosis was lactotroph cell adenoma with K i-67 labeling index of 28.9% and positive immunoreactivity for p53. This case could be diagnosed as a high-risk adenoma from the beginning of treatment based on the WHO 2017 criteria, but the clinical course was unusually long and the indication of aggressive adjuvant therapy after initial surgery remained unsolved. Conclusion: Pathologic confirmation for the present definition would be expected to assess the cutoff between typical adenomas and aggressive tumors.