Pituitary carcinomas are extremely rare accounting for only 0.1%0.2% of all pituitary tumours. The diagnosis is primarily dependent on aggressive imaging characteristics and high tumour mitotic activity on histology. A 47 year old gentleman with Type 1 Diabetes presented with an apparent non-functioning pituitary macro adenoma which was resected transsphenoidally and followed by EBRT. Initial histology was negative for ACTH. He presented 2 years later with florid Cushings syndrome. Bilateral adrenalectomy was performed in view of the absence of a definitive pituitary surgical target. The patient subsequently presented with marked weight loss and progressive generalised hyperpigmentation suggestive of Nelsons syndrome. ACTH levels were moderately elevated at 67 ng/l. Cranial imaging excluded a recurrence of pituitary tumour. Whole body CT revealed a large hepatic lesion with portocaval lymphadenopathy. ACTH precursor levels were markedly elevated at 159 750 (Normal range <40). The liver lesion was surgically resected and histopathology was positive for synaptophysin and ACTH with features indicative of a neuroendocrine tumour. Ki67 proliferation index was 21%. Retrospective review of initial pituitary histology showed positive staining for ACTH and Ki67 index of 13% suggesting metastatic pituitary carcinoma.
Conclusion: Pituitary carcinomas are extremely rare accounting for 0.1%0.2% of all pituitary tumours. Invasive Pituitary adenomas with a Ki67 proliferation index >3% should be followed up closely. Diagnostic molecular markers and cancer immunotherapy drugs offer additional treatment options in cases where re-do pituitary surgery or stereotactic radiotherapy are contraindicated. A high index of suspicion remains the cornerstone of diagnosis.