UNEXPECTED IMMUNOHISTOCHEMICAL SURPRISE OF A CUSHINGS DISEASE MACROADENOMA CO-EXPRESSING ACTH AND PROLACTIN: A CASE REPORT

Pituitary adenomas (PA) are benign well-differentiated tumors, with monoclonal development from the anterior pituitary gland, which can result in serious complications, in particular endocrine, metabolic and visual. Mixed ACTH and prolactin- secreting pituitary adenomas (PA) represent a rare association. We report a rare case of a patient who has Cushings disease with macroadenomaand the immunohistochemistry surprisinglyrevealed a co-expression of ACTH and PRL, with a silent prolactin lineage. She was a 41 years old female, admitted with aCushing syndrome ACTH-dependent of 73.63pg/ml, complicated with diabetes, dyslipidemia and hypertension. The hypothalamic-pituitary MRI revealed an 11.4x7 mm minimally invasivemacroadenoma,and thevisual fieldwas slightly reduced in both eyes. Her PRL level was normal. She had undergone transsphenoidal removal of the tumor. The immunohistochemical study showed90% expression of ACTHantibodies and 10% of PRL antibodies, the KI67 proliferation index was at 5%. The outcomes showedregression of clinical syndrome with persistent biological cortisolic activity, and the MRI performed 8 months later was normal. Immunohistochemistry remains the key element in diagnosing pituitary tumors and orientating their management. Mixed adenomas, in particularACTH co-secreting adenomas are difficult to manage because of their higher risk of recurrence and their secretory features.