The 4th edition of the World Health Organization (WHO) classification of endocrine tumors has been recently released. In this new edition, major changes are recommended in several areas of the classification of tumors of the anterior pituitary gland (adenophypophysis). The scope of the present manuscript is to summarize these recommended changes, emphasizing a few significant topics. These changes include the following: (1) a novel approach for classifying pituitary neuroendocrine tumors according to pituitary adenohypophyseal cell lineages; (2) changes to the histological grading of pituitary neuroendocrine tumors with the elimination of the term “atypical adenoma;” and (3) introduction of new entities like the pituitary blastoma and re-definition of old entities like the null-cell adenoma. This new classification is very practical and mostly based on immunohistochemistry for pituitary hormones, pituitary-specific transcription factors, and other immunohistochemical markers commonly used in pathology practice, not requiring routine ultrastructural analysis of the tumors. Evaluation of tumor proliferation potential, by mitotic count and Ki-67 labeling index, and tumor invasion is strongly recommended on individual case basis to identify clinically aggressive adenomas. In addition, the classification offers the treating clinical team information on tumor prognosis by identifying specific variants of adenomas associated with an elevated risk for recurrence. Changes in the classification of non-neuroendocrine tumors are also proposed, in particular those tumors arising in the posterior pituitary including pituicytoma, granular cell tumor of the posterior pituitary, and spindle cell oncocytoma. These changes endorse those previously published in the 2016 WHO classification of CNS tumors. Other tumors arising in the sellar region are also reviewed in detail including craniopharyngiomas, mesenchymal and stromal tumors, germ cell tumors, and hematopoietic tumors. It is hoped that the 2017 WHO classification of pituitary tumors will establish more biologically and clinically uniform groups of tumors, make it possible for practicing pathologists to better diagnose these tumors, and contribute to our understanding of clinical outcomes for patients harboring pituitary tumors.

世界卫生组织（WHO）内分泌肿瘤分类的第4版最近已发布。在这个新版本中，建议在垂体前叶肿瘤（腺垂体）分类的几个领域进行重大更改。本手稿的范围是总结这些建议的更改，并强调一些重要的主题。这些变化包括：（1）根据垂体腺垂体细胞谱系对垂体神经内分泌肿瘤进行分类的新方法；（2）消除“非典型腺瘤”一词，改变垂体神经内分泌肿瘤的组织学分级；（3）引入新的实体，例如垂体母细胞瘤，重新定义旧的实体，例如空细胞腺瘤。这种新的分类非常实用，主要基于垂体激素，垂体特异性转录因子和病理学实践中常用的其他免疫组化标记物的免疫组织化学，不需要常规的肿瘤超微结构分析。强烈建议根据具体情况通过有丝分裂计数和Ki-67标记指数评估肿瘤的增殖潜力，以鉴定临床上具有侵袭性的腺瘤。另外，该分类通过鉴定与复发风险增加相关的腺瘤的特定变体，提供了有关肿瘤预后的治疗性临床团队信息。还提出了非神经内分泌肿瘤分类的改变，特别是那些发生在垂体后叶的肿瘤，包括上皮细胞瘤，垂体后叶颗粒细胞瘤和梭形细胞瘤。这些变化支持先前在2016年WHO WHO CNS肿瘤分类中公布的变化。还详细审查了在鞍区出现的其他肿瘤，包括颅咽管瘤，间质和基质肿瘤，生殖细胞肿瘤和造血肿瘤。希望2017年WHO对垂体肿瘤的分类将建立更多生物学上和临床上统一的肿瘤组，使执业病理学家能够更好地诊断这些肿瘤，并有助于我们对患有垂体瘤的患者的临床结局有所了解。还详细审查了在鞍区出现的其他肿瘤，包括颅咽管瘤，间质和基质肿瘤，生殖细胞肿瘤和造血肿瘤。希望2017年WHO对垂体肿瘤的分类将建立更多生物学上和临床上统一的肿瘤组，使执业病理学家能够更好地诊断这些肿瘤，并有助于我们对患有垂体瘤的患者的临床结局有所了解。还详细审查了在鞍区出现的其他肿瘤，包括颅咽管瘤，间质和基质肿瘤，生殖细胞肿瘤和造血肿瘤。希望2017年WHO对垂体肿瘤的分类将建立更多生物学上和临床上统一的肿瘤组，使执业病理学家能够更好地诊断这些肿瘤，并有助于我们对患有垂体瘤的患者的临床结局有所了解。