トルコ鞍部腫瘍の分類・診断

Histological Classification and Diagnosis of Sellar/Parasellar Tumors

Point

・臨床病理学的見地から，下垂体腺腫は下垂体神経内分泌腫瘍（PitNET）へ名称が変更された．

・PitNETの組織分類の基本は，下垂体転写因子（PIT1, TPIT, SF1）の免疫組織化学になった．

・腫瘍増殖能の指標（Ki67指数）の有用性や，特定の組織型の腫瘍がaggressiveな臨床経過を呈しやすいことは示されたが，PitNETのgrade分類は提示されなかった．

・エナメル上皮腫型と乳頭型の頭蓋咽頭腫は，おのおのCTNNB1変異とBRAF変異を呈する独立した個別の組織型になった．

・下垂体細胞腫，顆粒細胞腫などTTF1陽性の4型の後葉（神経下垂体）腫瘍は，下垂体細胞（pituicyte）由来腫瘍として統一された．

　In the 5^th edition of the WHO classification of pituitary tumors, there are several significant changes:（1）the nomenclature has evolved from“pituitary adenoma”to“pituitary neuroendocrine tumor”（PitNET）;（2）PitNETs are now categorized in detail based on tumor lineage, cell type, and related characteristics;（3）the routine use of pituitary transcription factor（PIT1, TPIT, SF1）immunohistochemistry for PitNET classification;（4）there is a distinction between two types of craniopharyngioma（CP）, adamantinomatous CP and papillary CP, characterized by CTNNB1（β-catenin）and BRAF mutations, respectively;（5）the integration of four subtypes of posterior lobe（neurohypophysial）tumors, known as the family of pituicyte tumors that express TTF1, is emphasized.

　Regarding tumor proliferation markers, the assessment of the Ki-67 proliferation index remains important, although no specific cutoff value was provided. Certain PitNET subtypes have been recognized as clinically more aggressive, referred to as high-risk PitNETs. However, it is worth noting that the classification does not introduce a new grading system for PitNETs.