# Thyrotroph Pituitary Neuroendocrine Tumors: Molecular Pathology, Diagnostic Challenges, and Receptor-Targeted Therapeutic Strategies

## TL;DR

This review discusses the biology, diagnosis, and treatment of rare TSH-producing pituitary tumors, emphasizing receptor-targeted therapies for better management.

## Contribution

The paper highlights advances in lineage-based classification and receptor profiling for personalized treatment of thyrotroph PitNETs.

## Key findings

- Thyrotroph PitNETs show strong expression of somatostatin receptor subtype 2, making them responsive to receptor-targeted therapy.
- These tumors lack common driver mutations but exhibit heterogeneous molecular alterations involving cell-cycle and signaling pathways.
- Accurate differentiation from resistance to thyroid hormone β is critical for appropriate treatment strategies.

## Abstract

Thyrotroph pituitary neuroendocrine tumors (PitNETs), also known as thyroid-stimulating hormone (TSH)-producing pituitary adenomas (TSHomas), are rare functional pituitary tumors that cause excessive thyroid hormone production. These tumors are often difficult to cure by surgery alone, because they are frequently large or invasive at diagnosis. A key biological feature of thyrotroph PitNETs is their high expression of somatostatin receptor subtype 2, which makes them particularly sensitive to somatostatin receptor ligand therapy. Recent advances in tumor classification and molecular pathology have improved our understanding of their tumor biology and therapeutic vulnerabilities. This review summarizes current knowledge of the molecular mechanisms, pathological features, diagnostic challenges, and treatment strategies for thyrotroph PitNETs, with a focus on receptor-targeted therapies that bridge tumor biology and clinical management.

Thyrotroph pituitary neuroendocrine tumors (PitNETs) are rare functional pituitary tumors characterized by autonomous secretion of thyroid-stimulating hormone (TSH), leading to central hyperthyroidism. Under the 2022 World Health Organization classification, these tumors are defined as PIT1-lineage PitNETs, reflecting lineage-specific differentiation and improving pathological accuracy. Clinically, thyrotroph PitNETs often present as macroadenomas with invasive growth, making complete surgical resection challenging and necessitating multimodal treatment strategies. From a molecular oncology perspective, thyrotroph PitNETs lack recurrent driver mutations and instead exhibit heterogeneous alterations involving dysregulated cell-cycle control, impaired thyroid hormone-mediated negative feedback, and aberrant growth factor signaling. Immunohistochemically, tumor cells express PIT1 and TSH and show strong membranous expression of somatostatin receptor subtype 2, providing a biological rationale for somatostatin receptor ligand -based therapy. Somatostatin receptor ligands play a central role in the management of thyrotroph PitNETs as preoperative, adjuvant, or primary treatment and achieve effective hormonal control and tumor stabilization or shrinkage in many patients. Accurate differentiation between thyrotroph PitNETs and resistance to thyroid hormone β is essential, as these entities share biochemical features but require fundamentally different management. Advances in lineage-based tumor classification, receptor profiling, and molecular pathology have refined diagnostic strategies and enabled a more personalized, tumor-oriented therapeutic approach. This review highlights current insights into the tumor biology and treatment of thyrotroph PitNETs and discusses future perspectives for receptor-targeted and molecularly informed therapies.