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PH-RS11

Pleural tumours

How asbestos fibres and lost tumour suppressors such as BAP1 turn mesothelial cells into mesothelioma, how its three types look, how it encases the lung, and how solitary fibrous tumours and metastases differ.

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  • 4 steps · 10 questions
  • 3D normal anatomy

By the end, you can

  • Describe the mesothelium and explain why mesothelial cells can form epithelial-like or spindle-cell tumours.
  • Explain how amphibole asbestos fibres, chronic inflammation and loss of BAP1 and CDKN2A lead to mesothelioma after a long latency.
  • Compare epithelioid, biphasic and sarcomatoid mesothelioma, and explain how mesothelioma is told apart from reactive mesothelium and metastatic adenocarcinoma.
  • Relate the local growth of mesothelioma and of pleural metastases to effusion, breathlessness, pain and staging.
  • Describe solitary fibrous tumour of the pleura, its NAB2::STAT6 fusion and its effect on blood glucose.
  • Recognise the classic appearances, stains, classification and tests of pleural tumours, and explain how surgery, chemotherapy, checkpoint inhibitors, radiotherapy and pleurodesis act on them.

What it is

Pleural tumours are tumours of the pleura and its mesothelial lining. The main primary tumour is mesothelioma, a malignant tumour of mesothelial cells, usually caused by asbestos; the WHO 5th edition calls the usual form diffuse pleural mesothelioma, divided into epithelioid, biphasic and sarcomatoid types. Solitary fibrous tumour arises from the connective tissue beneath the mesothelium. Secondary tumours (metastases), mainly from the lung and breast, are far commoner than primary ones.

4 types to tell apart
Diffuse pleural mesothelioma
Malignant tumour of mesothelial cells that encases the lung; epithelioid, biphasic or sarcomatoid; usually asbestos-related, with a latency of decades.
Mesothelioma in situ
A flat surface layer of mesothelial cells with BAP1 or CDKN2A loss but no invasion; a recently recognised precursor.
Solitary fibrous tumour
Fibroblastic tumour, usually on a stalk from the visceral pleura, with a NAB2::STAT6 fusion; mostly benign.
Secondary pleural tumours
Metastases, mainly from lung and breast carcinoma, lymphoma, ovary and stomach; the commonest cause of a malignant effusion.

US spelling: tumours → tumors, tumour → tumor.

Normal function

The pleura and its mesothelial lining

The has two layers: the visceral pleura covering the lungs and the parietal pleura lining the chest wall, and mediastinum. A thin film of fluid between them lets the lungs glide. Fluid filters slowly from capillaries and drains through small openings (stomata) in the parietal pleura into lymphatics that run to the mediastinal and internal thoracic nodes. The lowest part of the space is the .

Both layers are covered by mesothelium, a single layer of flat mesothelial cells whose microvilli and secreted glycoproteins and hyaluronan keep the surfaces slippery. Mesothelium comes from the mesoderm and has features of two tissues: like epithelium, its cells contain cytokeratins and are joined by tight junctions, yet they also contain vimentin and, when injured, can become spindle cells that lay down collagen. They stain for calretinin, WT1 and D2-40 (podoplanin), markers used to recognise mesothelial tumours.

The same lining covers the peritoneum, the pericardium and the tunica vaginalis of the testis, so mesothelioma can arise in any of them, most often in the pleura. Beneath it, loose connective tissue holds fibroblasts, vessels and lymphatics.

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