Primary resistance to Cabergoline occurs in a minority of patients with lactotroph adenomas but the development of late resistance following initial response is an extremely rare phenomenon which has only been reported in very few cases.: We report the case of a 57 year old lady who was presented in 1997 with headaches and visual failure and was found to have a large pituitary mass with compression of the optic chiasm and invasion into the cavernous sinuses bilaterally. Serum prolactin concentration was over 100,000 mIU/L (normal range 50300 mIU/L). She was initially treated with bromocriptine but was later changed to cabergoline 2 mgs per week because of gastrointestinal intolerance. Serum prolactin dropped to a nadir of 1,610 mIU/L and her vision returned to normal. Repeat imaging one year later showed an empty sella with no evidence of a residual tumour.
Four years later, prolactin level started to rise reaching a peak of 22,330 mIU/L despite an increase in cabergoline dose to 6 mgs per week. Repeat MRI showed a large invasive pituitary mass with optic chiasm compression which was associated with bitemporal superior quadrantopia. There was no evidence of metastatic deposits. Lack of compliance with treatment was outruled by supervised drug administration. She underwent surgical excision of the tumour. The specimen histology was consistent with a prolactinoma with negative p53 and less than 3% ki-67 staining.
This is a very unusual case of a lactotroph adenoma with initial complete regression after cabergoline therapy but recurrence four years later on treatment. Physicians should aware of the possibility of secondary resistance to dopamine agonist therapy in lactotroph adenomas which has been linked to malignant transformation. Long-term careful monitoring is mandatory in all such patients.