Loss of ATRX Protein Expression in an Aggressive Null Cell Pituitary Tumor.

Somatic alpha thalassemia/mental retardation syndrome X-linked (ATRX) pathogenic variants have been shown to predict a malignant phenotype in neuroendocrine tumors. They were recently identified in aggressive pituitary tumors and carcinomas, mainly of corticotrophic origin. To our knowledge, these tumors are rare in a general cohort of pituitary tumors, with no cases described in null cell tumors. These variants can lead to loss of protein expression as revealed by immunohistochemistry. We describe a case of an aggressive null cell pituitary tumor with loss of ATRX expression. The patient underwent two transsphenoidal surgeries and radiotherapy and exhibited tumor growth despite conventional therapy. Analysis of the tumor samples revealed loss of ATRX expression in both surgical specimens, suggesting that ATRX may be a useful biomarker for the early identification of aggressive pituitary tumors.