Receptor imaging with In-111-pentreotide and(123)I-methoxybenzamide, and inhibition tests with octreotide and bromocriptine of mixed growth hormone/prolactin-secreting pituitary tumors

We have performed pituitary scintigraphy with In-111-pentreotide (OCT), a s omatostatin analogue, and with metoxybenzamide (IBZM) by I-123-IBZM in two patients affected by mixed growth hormone/prolactin-secreting pituitary tum ors. Short-term growth hormone (GH) inhibition by a single injection of OCT (100 mu g sc), and short-term prolactin (PRL) inhibition by oral administr ation of 2.5 mg of bromocriptine (BCR), were also performed in both patient s. The first patient, a 26 year old man, showed intense tumor uptake of I-123- IBZM scintigraphy, whereas In-111-OCT scintigraphy showed moderate tumor up take. Five hours after the BCR inhibition test, a fall of 83% in PRL plasma levels (from 8,336 mu g/L to 1,417 mu g/L), and of 91.6% in GH plasma leve ls (from 39.5 mu g/L to 3.3 mu g/L) were observed. OCT inhibition test supp ressed GH plasma levels from 36 mu g/L to 3.5 mu g/L. The patient was submi tted to treatment with BCR and OCT. A dramatic shrinkage of the tumor was s een after six months of therapy. The lesion disappeared one year after the start of therapy. The second patient, a 64 year old man, showed intense uptake at In-111-OCT scintigraphy, while I-123-IBZM uptake was not observed. A test dose of BCR resulted in an acute fail of PRL (from 145 mu g/L to 118 mu g/L), but not o f GH. A test dose of OCT decreased the GH plasma level from 61 mu g/L to 4. 5 mu g/L. The patient was submitted to treatment with BCR and OCT that resu lted in a computed tomography and magnetic resonance imaging decrease of 45 % of tumor volume one year after the start of therapy. Our results suggest that both suppression tests with OCT and BCR, and scint igraphic studies in vivo with In-123-IBZM and In-111-OCT can be predictive for the effectiveness of therapies with dopamine agonists and/or SS-analogs in patients with mixed PRL/GH-secreting pituitary tumors. Further studies are required to evaluate the role of suppressive tests in selecting patient s for appropriate clinical treatments. (C) 1999 Elsevier, Paris.