POU1F1 and TSH-secreting pituitary adenoma: PitNETs are classified by their lineage-restrictive pituitary transcription factors (i.e., TPIT for corticotroph adenomas; PIT1 for somatotroph, lactotroph, and thyrotroph adenomas; SF1 for gonadotroph adenomas; and absence of PIT1, TPIT, and SF1 for null cell adenomas), which were first delineated in the 2017 World Health Organization (WHO) classification guideline and preserved in the 2022 guidelines [41,42].