SOMATOSTATIN RECEPTOR SUBTYPES, OCTREOTIDE SCINTIGRAPHY, AND CLINICAL-RESPONSE TO OCTREOTIDE TREATMENT IN PATIENTS WITH NEUROENDOCRINE TUMORS

Several types of neuroendocrine tumor express high numbers of somatost atin receptors (sstr). We have compared the express:ion of sstr subtyp es with the outcome of octreotide scintigraphy in patients with carcin oids and medullary thyroid carcinoma (MTC) in comparison with Hurthle cell tumors. The effect of sstr activation (octreotide treatment) on t umor markers was also studied in patients with disseminated carcinoid tumors. Six patients with carcinoid tumors (four midgut and two foregu t), and three patients with thyroid tumors (one MTC, one Hurthle cell carcinoma, and one Hurthle cell adenoma) were studied. Octreotide scin tigraphy visualized tumor sites in all nine patients. Macroscopic tumo r was verified at these sites at subsequent surgical exploration. Usin g Northern blotting and subtype-specific riboprobes, sstr could lie de tected in all tumors examined. All five sstr subtypes were detected in most of the carcinoid tumors. All six carcinoids expressed sstr2., Th is was in contrast to the findings for the thyroid tumors analyzed, wh ich also expressed several sstr subtypes but in some cases lacked expr ession of sstr2. This was also the case for normal thyroid tissue. Cli nically, octreotide treatment of the patients with midgut carcinoid tu mors resulted in palliation of hormonal symptoms accompanied by a sign ificant reduction of urinary 5-HIAA levels (28-71%). These results ind icate that carcinoid tamers frequently express all five sstr subtypes, The thyroid tumors also expressed multiple sstr but could lack expres sion of sstr2., Nevertheless, these tumors were visualized by octreoti de scintigraphy, indicating that sstr2 expression is not a prerequisit e for tumor imaging.