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WHO Classification of Tumours
Atypical adenoma
Pituitary gland


Some pituitary adenomas have atypical morphologic features suggestive of aggressive behaviour such as invasive growth. Other features include an elevated mitotic index and a Ki-67 labeling index greater than 3%, as well as extensive nuclear staining for TP53 immunoreactivity. These features are usually lacking in noninvasive adenomas and are present in nearly all pituitary carcinomas. Tumours with these features that have no documented metastases can be designated as “atypical” adenomas
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Ronald A. DeLellis, Ricardo V. Lloyd, Philipp U. Heitz, Charis Eng
World Health Organization Classification of Tumours. Pathology and Genetics of Tumors of Endocrine Organs
IARC Press: Lyon 2004