Discussion

Mixed somatotroph-lactotroph pituitary adenomas are well recognized. Up to 25% of pituitary tumors in patients with acromegaly may show mixed features. A recent review by Kreutzer and colleagues demonstrates that as many as 50% of all "somatotrophic" tumors are also immunopositive for prolactin.

Several features of our patient's case merit further discussion. He presented with clinically advanced acromegaly, as indicated by the history and physical examination, hormonal profile, and radiographic evidence of a macroadenoma. Although surgery was undoubtedly the first option for treatment, the chances for cure in this patient were low because of the tumor size and its extension. It is somewhat surprising that -- using the most recent criteria for remission -- this patient may be considered cured of acromegaly. This may be because GH production was restricted to a relatively small component of the tumor, as demonstrated by immunohistochemistry, so that even a partial resection resulted in reduction of serum GH levels to the normal range.

The extremely elevated prolactin levels, together with the strong immunostaining for prolactin in the majority of adenoma cells, indicated that the tumor had a significant lactotrophic component. In spite of the surgical success in relation to acromegaly, the persistently elevated serum prolactin levels and the postsurgical MRI findings confirmed the persistence of a large macroprolactinoma. A second surgical procedure was not the next option for treatment, because of the known efficacy of medical therapy with dopamine agonists. In this patient, medical management has adequately maintained a normal serum prolactin level and has stabilized residual tumor size since the surgery was performed 2 years ago.

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