Cancers Most Likely to Metastasize to the Lung
Colorectal cancer, breast cancer, thyroid cancer, head and neck squamous cell carcinomas, sarcomas, and renal cell carcinoma are the primary malignancies most likely to metastasize to the lungs. 1, 2
High-Risk Primary Cancers for Lung Metastasis
The British Thoracic Society guidelines stratify cancers by their propensity to metastasize to the lung, identifying specific high-risk groups 3:
Group 5 (Highest Metastatic Risk to Lung):
- Kidney (renal cell carcinoma)
- Thyroid carcinoma
- Colon carcinoma
- Adrenal gland carcinomas
- Salivary gland carcinomas
- Uterine carcinomas
- Thymic tumors
These cancers demonstrated the highest likelihood of lung nodules being metastatic rather than new primary lung cancers in multivariate analysis 3.
Additional High-Risk Primaries:
- Colorectal cancer frequently metastasizes to lungs with a distinctive immunohistochemical profile (TTF-1 negative, CK7 negative, CK20 positive, CDX-2 positive) 1
- Breast cancer commonly spreads to lungs, particularly basal-like breast cancer which shows lung tropism 1, 4
- Sarcomas frequently metastasize solely to the lungs, and isolated lung metastases may be surgically resectable for cure 1, 2
- Head and neck squamous cell carcinomas commonly spread to lungs and can mimic primary lung squamous cell carcinoma 3, 1
Intermediate-Risk Cancers
Groups 1-3 (More Likely to Develop New Primary Lung Cancer):
When lung nodules appear in patients with these cancers, they are more likely to represent new primary lung cancers rather than metastases 3:
- Squamous cell cancers of head and neck
- Lymphoma or leukemia
- Bladder, breast, cervical, biliary, esophageal, ovarian, prostate, or gastric carcinomas
Key Distinguishing Features
Radiographic Patterns:
- Metastatic tumors from breast, colon, and prostate show expansile growth rather than infiltrative growth 3, 1
- Primary lung cancers demonstrate infiltrative growth with adjacent lung retraction and pleural involvement 3
Clinical Context Matters:
In surgical series of resected pulmonary metastases, the most common primary sites were thyroid, colon, breast, genitourinary tract, skin, liver, and adrenal glands 2. Up to half of autopsies performed on patients who died of malignancy demonstrate pulmonary metastases 2.
Critical Diagnostic Pitfall
Do not assume all lung nodules in cancer patients are metastases. In patients with known extrapulmonary cancer referred for lung nodule resection, 58% were actually new primary non-small cell lung cancer, not metastases 3. This is particularly true for patients over 55 years old who smoke and have breast or prostate cancer as their known primary 3.
Anatomical Explanation
The lung's unique characteristics make it the most common site for metastases: it receives the entire cardiac output every minute, has the densest capillary bed in the body, and is the first reservoir for most lymphatic drainage entering the venous system 2.