PREOPERATIVE OCTREOTIDE TREATMENT OF GROWTH HORMONE-SECRETING AND CLINICALLY NONFUNCTIONING PITUITARY MACROADENOMAS - EFFECT ON TUMOR VOLUME AND LACK OF CORRELATION WITH IMMUNOHISTOCHEMISTRY AND SOMATOSTATIN RECEPTOR SCINTIGRAPHY

The factors that determine the hormone and volume responses of pituita ry adenomas to the somatostatin analog octreotide are poorly understoo d. We, therefore, studied the correlation between (111)indium-pentetre otide somatostatin receptor scintigraphy (SRS) and the clinical and im munohistochemical classification of pituitary adenomas, on the one han d, and hormone and volume responses, on the other hand. Ten patients w ith GH-secreting (6 females and 4 males; age, 31-67 yr) and 14 patient s with clinically nonfunctioning (NF) macroadenomas (5 females and 9 m ales; age, 22-79 yr) were preoperatively treated with 300 mu g/day oct reotide, which was increased to 600 and 1500 mu g/day at weekly interv als and then continued for at least 3 months until surgery. SRS was pe rformed before therapy. A sellar magnetic resonance imaging scan was p erformed before therapy; 1, 2, and 3 weeks and 3 months after start of therapy; and after surgery. Acromegalics also had an 8-h GH profile, insulin-like growth factor-I determination, and a 100-g oral glucose l oad at these time points. An attempt was made to identify NF adenomas as gonadotroph adenomas using their LH, FSH, and cu-subunit responses to TRH. In acromegalic patients, octreotide suppressed mean GH (8-h pr ofile) and insulin-like growth factor-I concentrations from 34.9 +/- 9 .7 to 8.1 +/- 3.6 mu g/L and from 2122 +/- 1025 to 701 +/- 208 mu g/L, respectively, after 3 months. Significant (26-85% decline) tumor shri nkage occurred in 5 of 10 patients, mainly within the first week. Tumo r shrinkage and GH suppression were not correlated. Four of 7 patients had increased pituitary (111)indium-pentetreotide uptake, but this di d not predict GH suppression or tumor shrinkage. Of the NF adenomas, 2 responded with shrinkage (57% and 96% decline). Four of 12 adenomas h ad increased (111)indium-pentetreotide uptake, but this did not correl ate with tumor shrinkage (2 adenomas: I gonadotroph and 1 null cell ad enoma), immunohistochemistry, or clinical classification. We conclude that preoperative octreotide therapy suppresses GH in most patients an d reduces tumor volume in up to 50% of acromegalic patients. It also i nduces shrinkage in some NF adenomas, although less frequently. SRS do es not predict shrinkage of either tumor type. Shrinkage does not corr elate with clinical classification or immunohistological characteristi cs. Further studies are needed to identify the factors that determine the hormone and volume responses of pituitary adenomas to octreotide t herapy.