The WHO Classification of Thoracic Tumors (5(th) edition) mainly has the following changes in the chapter of pleural malignant mesothelioma. (1) The concept of mesothelioma in situ and its diagnostic method have been established for the first time; (2) The tumour grading of pleural malignant mesothelioma was added, it was divided into low grade and high grade according to the cellular atypia, mitotic activity and presence of necrosis. (3) The morphological features of pleural malignant mesothelioma was classified into architectural pattern, cellular and stromal features, the correlation between histological features and prognosis was refined, and some of the controversial cellular types have been reclassified. In this review, we introduced the changes of related pathologic diagnosis, in the WHO Classification of Thoracic Tumors (5(th) edition) and discussed its clinical significance.
《WHO胸部肿瘤分类（第五版）》在胸膜恶性间皮瘤部分主要有以下几点变化：1.确立了原位间皮瘤的概念及其诊断方法；2.新增了胸膜恶性间皮瘤的肿瘤分级，即根据上皮样间皮瘤的细胞异型性、核分裂活性及有无坏死分为低级别和高级别；3.把胸膜恶性间皮瘤的组织学特征分为组织结构、细胞及间质特征，细化了组织学特征与预后的相关性，同时对部分有争议的组织学形态进行了归类。本文主要围绕新版WHO分类病理学诊断相关的主要变化，对其临床意义进行了讨论。.
Keywords: 5(th) WHO classification; Histological grading; Mesothelioma; Mesothelioma in situ; Pathological diagnosis; Pleural malignant mesothelioma.