Expression of type 5 somatostatin receptor in TSH-secreting pituitary adenomas: a possible marker for predicting long-term response to octreotide therapy.
In TSH-secreting pituitary adenomas (TSHoma), octreotide (OCT) therapy reduces tumor size and TSH secretion in some cases but not in others. As OCT acts through various types of somatostatin receptors (SSTRs), the different responses of TSHoma to OCT might be explained by the differences of SSTR expression. We therefore studied the expression of subtype-specific SSTR mRNA transcripts in tumor tissues by RT-PCR. Type 2 (SSTR2) mRNA transcripts were detected in all 8 tumors but those of SSTR3 and SSTR5 were demonstrated only in 5 of them. Serum TSH levels were decreased by OCT administration test in all patients but OCT therapy was effective in two patients out of three. SSTR5 mRNA was detected in two tumors from the responder, but not in one tumor that was resistant to OCT. These observations suggest that the temporal decrease of TSH by OCT may be mediated by SSTR2, and that the long term response to OCT therapy may be related with the expression of SSTR5. Therefore, the expression of SSTR5 in TSHoma may be a useful marker for predicting the outcome of the therapy, but further studies with larger numbers of patients are necessary.
Yoshihara
Ai
A
Department of Medicine, Institute of Clinical Endocrinology, Tokyo Women's Medical University, Japan.
Isozaki
Osamu
O
Hizuka
Naomi
N
Nozoe
Yasuko
Y
Harada
Chie
C
Ono
Masami
M
Kawamata
Takakazu
T
Kubo
Osami
O
Hori
Tomokatsu
T
Takano
Kazue
K
D000236:Adenoma / Q000175:diagnosis / Q000188:drug therapy* / Q000235:genetics* / Q000378:metabolism; D018931:Antineoplastic Agents, Hormonal / Q000627:therapeutic use; D014408:Biomarkers, Tumor / Q000235:genetics*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D008297:Male; D015282:Octreotide / Q000627:therapeutic use*; D010911:Pituitary Neoplasms / Q000175:diagnosis / Q000188:drug therapy* / Q000235:genetics* / Q000378:metabolism; D011379:Prognosis; D020033:Protein Isoforms / Q000235:genetics; D017481:Receptors, Somatostatin / Q000235:genetics*; D013972:Thyrotropin / Q000097:blood / Q000378:metabolism*; D013995:Time; D016896:Treatment Outcome
D018931:Antineoplastic Agents, Hormonal; D014408:Biomarkers, Tumor; D020033:Protein Isoforms; D017481:Receptors, Somatostatin; C094573:somatostatin receptor 5; D013972:Thyrotropin; D015282:Octreotide