WHO胸膜肿瘤组织学分类(第5版，2021)：英文版

2021 WHO Classification of Tumors of the Pleura: ICD-O Coding and Terminology

Mesothelial tumors

Benign and preinvasive mesothelial tumors
Adenomatoid tumor  9054/0
Well-differentiated papillary mesothelial tumor  9052/1b
Mesothelioma in situ  9050/2c

Mesothelioma
Localized mesothelioma  9050/3b
Diffuse mesothelioma, NOS  9050/3b
Sarcomatoid mesothelioma  9051/3
Epithelioid mesothelioma  9052/3
Mesothelioma, biphasic  9053/3

2021 WHO Classification of Tumors of the Pleura: Essential and Desirable Diagnostic Criteria

Benign and preinvasive mesothelial tumors

Adenomatoid tumor

• Essential Criteria
  

• Focal proliferation of tubular spaces or vacuoles lined by flattened or cuboidal mesothelial cells in a fibrous stroma
• Lack of diffuse or multifocal spread along pleura and absence of malignant histologic features, such as invasive growth into underlying stroma, cytologic atypia, necrosis, or sarcomatoid patterns
  

• Desirable Criteria
  

• Immunohistochemistry for mesothelial markers, if needed
• Immunohistochemical staining for L1CAM, a marker of TRAF7 mutation, may be useful
• BAP1 expression retained and absence of homozygous deletion of CDKN2A
  

Well-differentiated papillary mesothelial tumor

• Essential Criteria
  

• Papillary stromal formations covered by bland mesothelium
• No stromal invasion
  

• Desirable Criteria
  

• Immunohistochemical staining for mesothelial markers
• BAP1 expression retained
  

Mesothelioma in situ

• Essential Criteria
  

• Pleural effusions (nonresolving)
• No thoracoscopic or imaging evidence of tumor
• Single layer of mesothelial cells (with or without atypia) on pleural surface
• No histologic features of invasive growth
• Loss of BAP1 and/or MTAP by immunohistochemistry and/or CDKN2A homozygous deletion by FISH
• Multidisciplinary discussion of diagnosis
  

• Desirable Criteria
  

• Papillary stromal formations covered by bland mesothelium
• No stromal invasion
  

Mesothelioma

Localized pleural mesothelioma

• Essential Criteria
  

• Presentation as a solitary localized mass by imaging, surgical findings, and histology
• Examination of a surgical resection specimen revealing lack of invasion beyond the circumscribed borders of the tumor
• Histologic features of diffuse mesothelioma
• Immunohistochemical evidence of mesothelial origin
  

• Desirable Criteria
  

• Multidisciplinary discussion to confirm the diagnosis
  

Diffuse pleural mesothelioma

• Essential Criteria
  

• Diffuse pleural thickening by a malignant neoplasm with epithelioid, sarcomatoid, or biphasic histology•
• Invasion of adjacent structures (i.e., adipose tissue, skeletal muscle, and/or lung parenchyma), tumor necrosis, or formation of unequivocal malignant tumor nodules
• Desmoplastic mesothelioma is characterized by dense collagenized tissue separated by malignant mesothelial cells arranged in a storiform or so-called patternless pattern, which must be present in ≥50% of the tumor in definitive resection specimens
• Biphasic mesothelioma is mesothelioma revealing ≥10% each of epithelioid and sarcomatoid patterns in definitive resection specimens or any percentage of each component in smaller biopsy and cytology specimens
• Immunohistochemistry confirming mesothelial origin
  

• Desirable Criteria
  

• Loss of BAP1 and/or MTAP by immunohistochemistry, and/or CDKN2A loss by FISH
• Or mutations in BAP1 or CDKN2A demonstrated by next-generation sequencing
  
  

The 2015 WHO classification6 recognized promising advances in the field of mesothelioma pathology, including histologic features with prognostic significance, nuclear grading of epithelioid diffuse pleural mesothelioma, and the use of BAP1 immunohistochemistry (IHC) and homozygous deletion of CDKN2A (9p21; encoding p16) by fluorescence in situ hybridization (FISH) in the separation of mesothelioma from reactive mesothelial proliferations, but these advances were not thoroughly incorporated into the classification until 2021.1 Recent advances in the understanding of genomics of mesothelioma have led to increased recognition of a new entity, mesothelioma in situ (MIS), which was not formally recognized previously. Criteria for MIS have now been established and are included in the 2021 WHO classification.
Mesenchymal tumors of the pleura have been moved to a new chapter titled “Mesenchymal tumours of the thorax.” An additional section in the “Metastases” chapter titled “Metastasis to the pleura” was added to the 2021 classification. The 2021 WHO Classification of Thoracic Tumors also includes a new chapter “Genetic tumour syndromes involving the thorax,” which includes a section titled “BAP1 tumour predisposition syndrome.” A review to address updates in hematolymphoid tumors of the pleura and pericardium will be published separately.

FISH, fluorescence in situ hybridization.

ICD-O, International Classification of Diseases for Oncology.

• Morphology codes are taken from the ICD-O, third edition, second revision (ICD-O-3.2) (REF 1256).
• Behavior is coded
• /0 for benign tumors;
• /1 for unspecified, borderline, or uncertain behavior;
• /2 for carcinoma in situ and grade III intraepithelial neoplasia; and /3 for malignant tumors.
  

参考文献：
The 2021 WHO Classification of Tumors of the Pleura: Advances Since the 2015 Classification - PubMed (nih.gov)
WHO Classification of Tumours, 5th edition; volume 5, Tumours of the pleura and pericardium (2021).

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