Thyrotrophs in PIT1‐lineage Pituitary Neuroendocrine Tumours Without Syndrome of Inappropriate Secretion of Thyrotropin Stimulating Hormone

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OBJECTIVE: Many patients with pituitary neuroendocrine tumours (PitNETs) containing beta (β) thyroid-stimulating hormone (TSH)-immunopositive cells, without syndrome of inappropriate secretion of TSH (SITSH), show a significant reduction in TSH levels following surgical removal of the tumour-like functioning thyrotroph PitNET. We evaluated the pathophysiological and clinical characteristics of TSH-positive cells in PIT1-lineage PitNETs in patients without the syndrome of inappropriate secretion of TSH. DESIGN: Retrospective cohort study. PATIENTS AND MESUREMENTS: Overall, 165 patients diagnosed with PIT1-lineage PitNETs without SITSH between April 2018 and July 2023 at Moriyama Memorial Hospital were reviewed. They were categorised into three groups based on the rate of βTSH-immuno-positive cells in their PitNETs: strongly positive group with 10% or more βTSH-immuno-positive cells, weakly positive group with less than 10%, and negative group. Clinical data from these groups were compared. RESULTS: Patient age, sex, and tumour size did not differ significantly among the groups. Most of the weakly positive cases had acromegaly, whereas many of the strongly positive cases had clinically nonfunctioning tumours. Preoperative TSH levels were slightly higher in strongly positive cases than in the other groups but fell within the normal range postoperatively, whereas postoperative TSH levels were significantly lower across all groups. The degree of TSH reduction postoperatively was significantly higher in the strongly positive group. CONCLUSIONS: In the strongly positive group, TSH levels decreased significantly after surgery, whereas no such decrease was observed in the other two groups, suggesting that thyrotrophs in strongly positive PitNETs are TSH-producing, similar to clinically functioning thyrotroph PitNETs.

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