Pasireotide therapy in a rare and unusual case of plurihormonal pituitary macroadenoma

We report the use of pasireotide in a rare and unusual case of pituitary macroadenoma co-secreting GH, prolactin and ACTH. A 62-year-old Caucasian man presented with impotence. Clinically, he appeared acromegalic and subsequent investigations confirmed GH excess and hyperprolactinaemia. Magnetic resonance imaging (MRI) of pituitary revealed a large pituitary macroadenoma. He underwent trans-sphenoidal surgery and histology confirmed an adenoma with immunohistochemistry positive for ACTH, GH and prolactin. Acromegaly was not cured following surgery and inadequately controlled despite subsequent octreotide therapy. He underwent further debulking pituitary surgery, following which IGF1 levels improved but still high. This time adenoma cells showed immunohistochemistry positivity for ACTH only, following which subsequent investigations confirmed intermittent hypercortisolaemia compatible with pituitary Cushing's disease. We recommended radiotherapy, but in view of the pluripotential nature of the tumour, we proceeded with a trial of s.c. pasireotide therapy on the basis that it may control both his acromegaly and Cushing's disease. After 3 months of pasireotide therapy, his mean GH and IGF1 levels improved significantly, with improvement in his symptoms but intermittent hypercortisolaemia persists. His glycaemic control deteriorated requiring addition of new anti-diabetic medication. MRI imaging showed loss of contrast uptake within the tumour following pasireotide therapy but no change in size. We conclude that our patient has had a partial response to pasireotide therapy. Long-term follow-up studies are needed to establish its safety and efficacy in patients with acromegaly and/or Cushing's disease. LEARNING POINTS: Plurihormonal pituitary adenomas are rare and unusual. Patients with pituitary adenomas co-secreting ACTH and GH are more likely to present with acromegaly because GH excess can mask hypercortisolaemia. Pasireotide holds potential where conventional somatostatin analogues are not effective in acromegaly due to higher affinity for somatostatin receptor subtypes 1, 2, 3 and 5. Significant deterioration in glycaemic control remains a concern in the use of pasireotide. Currently, long-term safety and efficacy of pasireotide in patients with acromegaly and/or Cushing's disease are not fully clear.