We have studied the relationship between mean pretreatment levels of serum
prolactin and the presence of positive immunohistochemical staining for
prolactin in the pituitary tumours of 55 patients. Pretreatment serum
prolactin was significantly higher in patients with tumours showing many
prolactin immunostaining cells than in those with none (P less than 0.001). When the pretreatment serum
prolactin exceeded 6000 mU/l, the tumours contained over 90% of
prolactin positive cells; one patient was an exception who had received long-term high dose
bromocriptine therapy, and her tumour showed only occasional cells with positive staining. When the pretreatment serum
prolactin level was under 2500 mU/l, a tumour was found which showed either no cells or fewer than 1% of cells which stained for
prolactin. There was no significant difference in pretreatment serum
prolactin levels between 11 patients with
craniopharyngiomas and 34 patients with pituitary macroadenomas showing no
prolactin immunostaining. Seventy-one percent (32) of the 45 patients with
craniopharyngiomas or tumours with negative immunostaining for
prolactin, had raised pretreatment serum
prolactin levels (above 360 mU/l) although this was usually only slightly elevated; the levels exceeded 2500 mU/l in six (13%) of them (two
craniopharyngiomas, four pituitary tumours) but in none did the levels exceed 6000 mU/l. Four of the 55 pituitary tumours showed occasional cells (less than 1%) that stained positively for
growth hormone. In none of the patients with these tumours was there evidence of
acromegaly or pathologically elevated circulating
growth hormone levels.