Other lung tumours and lung metastases
- Lesion
Not every lung nodule is carcinoma: hamartomas are benign coin lesions, and the lung is the most common site of metastases from other cancers.
What it is
Besides carcinomas and neuroendocrine tumours, the lung hosts benign and malignant mesenchymal and lymphoid tumours. Pulmonary hamartoma is the classic benign coin lesion; inflammatory myofibroblastic tumour affects children; lymphangioleiomyomatosis affects young women. The lung is the commonest site of metastatic cancer, usually as multiple peripheral nodules.
Structure
- Hamartoma: lobules of mature hyaline cartilage separated by clefts lined by respiratory epithelium, with fat and fibrous tissue.
- Inflammatory myofibroblastic tumour: firm grey-white mass of fascicles of spindle cells mixed with plasma cells and lymphocytes.
- Metastases: multiple rounded nodules that reproduce the histology of the primary; lymphangitic carcinomatosis fills lymphatics around bronchi and septa.
- Occasional lepidic growth by metastatic carcinoma can mimic adenocarcinoma in situ.
Step by step
- Metastatic cells reach the lung through the blood (the lung filters venous return from the whole body), lymphatics or direct invasion.
- Cells lodge in the capillary bed and grow into peripheral nodules.
- Carcinomas of breast, stomach, pancreas and colon may spread along lymphatics (lymphangitic pattern).
- Oesophageal carcinoma and mediastinal lymphoma can invade the lung directly.
Benign or uncommon lung tumours
| Tumour | Who | Key features |
|---|---|---|
| Pulmonary hamartoma | Adults, incidental | Cartilage, fat, epithelial clefts; popcorn calcification |
| Inflammatory myofibroblastic tumour | Children | Spindle myofibroblasts with plasma cells; ALK |
| Lymphangioleiomyomatosis | Young women | Cysts, TSC2 loss, mTOR |
| MALT lymphoma | Adults, autoimmune disease | Small B cells along bronchi (lymphoepithelial lesions) |
Clinical notes
- A solitary nodule with popcorn calcification and fat on CT is typical of hamartoma.
- Multiple nodules in a patient with a known cancer suggest metastases (common primaries: breast, colon, kidney, sarcomas, melanoma, germ cell tumours).
- Lymphangitic spread causes progressive dyspnoea out of proportion to imaging.
Test yourself
Think of the answer, then tap the question to see it.
What is a pulmonary hamartoma made of?
Nodules of mature cartilage, fat and fibrous tissue with clefts lined by respiratory epithelium; it is a clonal benign neoplasm.
Which site is the most common location of metastatic tumours?
The lung.
What is lymphangioleiomyomatosis?
A proliferation of perivascular epithelioid cells with TSC2 loss in young women, causing cystic lungs, pneumothorax and chylous effusions.
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Lung Cancer (MedlinePlus, US National Library of Medicine, 2025).
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Representative model, for educational purposes only.