POSITIVE SOMATOSTATIN RECEPTOR SCINTIGRAPHY CORRELATES WITH THE PRESENCE OF SOMATOSTATIN RECEPTOR SUBTYPE-2

Somatostatin receptor scintigraphy (SRS) is positive in approximately 75% of all patients with neuroendocrine gastroenteropancreatic tumours . This study aimed to identify specific somatostatin receptor (sstr) s ubtypes, which are responsible for the in vivo binding of the widely u sed somatostatin analogue, octreotide in human neuroendocrine gastroen teropancreatic tumours. Twelve patients underwent SRS with radiolabell ed octreotide. After surgical resection, tumour tissues were analysed in vitro for somatostatin and octreotide binding sites by autoradiogra phy. In addition, for the first time, sstr subtype mRNA expression was examined by semiquantitative reverse transcription polymerase chain r eaction (RT-PCR). Tumour tissues from all SRS positive patients were p ositive by autoradiography. Semiquantitative RT-PCR revealed most prom inently sstr2 expression in scintigraphically positive tumours. Two SR S negative tumours contained in vitro octreotide binding sites as well as high levels of sstr1 and sstr2 mRNAs. Positive SRS is mainly due t o sstr2. sstr1, 3, 4, and probably 5 are less important for in vivo oc treotide binding. False negative scintigraphic results seem to be infl uenced by factors independent of the expression of specific sstr.