Expression of type 5 somatostatin receptor in TSH-secreting pituitary adenomas: a possible marker for predicting long-term response to octreotide therapy
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Published on: April 17, 2019
Ai Yoshihara1, Osamu Isozaki, Naomi Hizuka
1Department of Medicine, Institute of Clinical Endocrinology, Tokyo Women's Medical University, Japan.
Abstract:
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.
Insights
Octreotide therapy effectiveness in TSH-secreting pituitary adenomas (TSHoma) varies. Somatostatin receptor subtype 5 (SSTR5) expression may predict treatment response, suggesting its potential as a predictive marker.
Area of Science:
- Endocrinology
- Oncology
- Molecular Biology
Background:
- TSH-secreting pituitary adenomas (TSHoma) are tumors affecting thyroid function.
- Octreotide (OCT) treatment efficacy in TSHoma varies, necessitating investigation into underlying mechanisms.
Purpose of the Study:
- To investigate the correlation between somatostatin receptor subtype (SSTR) expression and octreotide (OCT) treatment response in TSHoma.
- To determine if SSTR subtype mRNA expression can predict OCT therapy outcomes in TSHoma patients.
Main Methods:
- Tumor tissues from TSHoma patients were analyzed for SSTR subtype mRNA expression using RT-PCR.
- Correlation between SSTR expression profiles and clinical response to OCT therapy was assessed.
Main Results:
- All tumors expressed SSTR2 mRNA. SSTR3 and SSTR5 mRNA were detected in a subset of tumors.
- While OCT administration transiently decreased TSH in all patients, long-term OCT therapy was effective in only two out of three patients.
- SSTR5 mRNA was present in tumors of OCT responders but absent in the resistant tumor.
Conclusions:
- SSTR2 may mediate the acute TSH-lowering effect of OCT in TSHoma.
- SSTR5 expression appears to be a potential biomarker for predicting long-term OCT therapy response in TSHoma.
- Further research with larger cohorts is needed to validate SSTR5 as a predictive marker for TSHoma treatment.
