RESULTS OF SOMATOSTATIN RECEPTOR SCINTIGRAPHY DO NOT PREDICT PITUITARY-TUMOR VOLUME-RESPONSE AND HORMONE-RESPONSE TO OCTREOTIDE THERAPY ANDDO NOT CORRELATE WITH TUMOR HISTOLOGY

The value of somatostatin receptor scintigraphy (SRS) to predict the e ffect of somatostatin analog therapy on pituitary adenomas is not clea r, due to the use of different radiopharmaceuticals (I-123-Tyr(3)-octr eotide and In-111-pentetreotide) and the small number of patients in p revious studies, Mie used In-111-pentetreotide scintigraphy in 49 pati ents in order to (i) correlate SRS results with basal tumor volume as well as volume- and hormone-response to 3 months of octreotide therapy (Oct-Tx), (ii) identify tumor remnants after incomplete surgery and ( iii) evaluate any correlation with immunohistology. Twenty-five patien ts had a GH-secreting adenoma (GH-A, 15 prior to intended surgery, 10 with persistent/recurrent disease after previous therapy). Twenty-four patients had a clinically nonfunctioning adenoma (NF-A), For SRS, pla nar and single photon emission computer tomographic images (SPECT) wer e recorded 4 h and 24 h post injection. SRS grading was as follows: GO , no uptake; G1, uptake comparable to normal pituitary; G2, increased uptake; G3, very intense uptake, G2/3 was seen in 8/25 GH-A and in 12/ 24 NF-A. Pretreatment tumor volume (magnetic resonance imaging (MRI)) tended to be related to In-111-pentetreotide uptake in GH-A with a tum or visible on MRI (G0/1 (n=10) vs G2/3 (n=8): 3.6+/-1.9 vs 10.5+/-6.5 cm(3) (mean+/-S.E.), P=0.051), but not in NF-A (G0/1 (n=12) vs G2/3 (n =12): 17.0+/-10.1 vs 14.3+/-3.6 cm(3)), SRS did not identify a tumor r emnant in the 7 MRI-negative patients with persistent post-operative a cromegaly. Basal GH (6-h profile) and IGF-I in GH-A did not correlate with SRS results (G0/1 (n=17) vs G2/3 (n=8), GH: 32.3+/-18.2 vs 29.3+/ -7.4 mu g/l, IGF-I: 851+/-80 vs 1038+/-153 mu g/l). During Oct-Tx of G H-A neither tumor shrinkage nor GH suppression was related to SRS resu lts, In 6 NF-A classified as gonadotropinomas (by their plasma glycopr otein hormone or alpha-subunit concentrations, basally and/or in respo nse to TRH) In-111-pentetreotide uptake was not different from that of the non-gonadotropin/non-secreting adenomas. SRS results were not rel ated to the immunohistological subtype in 22 GH-A (monohormonal, mixed somatotrope/lactotrope, plurihormonal) or in 22 NF-A (null-cell adeno mas, gonadotropinomas, silent hormonal adenomas). We conclude that In- 111-pentetreotide SRS reflects tumor volume poorly in GH-A and not at ail in NF-A. It does not predict the effect of Oct-Tx on the volume of both GH-A and NF-A, nor on the GH concentration in GH-A. In-111-pente treotide SRS is unable to identify postoperative tumor remnants not vi sible on MRI.