What is the incidence of skin metastasis from a lung primary in patients with lung cancer, specifically non-small cell lung cancer (NSCLC)?

Skin Metastasis from Lung Cancer: Incidence and Clinical Significance

Skin metastasis from lung cancer is rare, occurring in approximately 1-5% of patients with lung cancer, though this represents a grave prognostic sign with median survival of only 4-5 months after cutaneous involvement is detected. 1, 2, 3

Incidence Data

The reported incidence of cutaneous metastasis from lung cancer varies across studies but consistently demonstrates rarity:

• 2.8% incidence in a large retrospective series of 2,130 advanced NSCLC patients at initial diagnosis 1
• 2.8% incidence in another clinical series of 579 lung cancer patients 4
• 4.9% incidence found at autopsy in a review of 510 primary lung cancer cases 2
• Range of 1-12% reported across multiple studies in the literature 3

Histologic Subtype Variations

Large cell carcinoma shows the highest propensity for skin metastasis, while squamous cell and small cell carcinomas demonstrate the lowest rates:

• Large cell carcinoma: 10.3% of patients develop cutaneous metastases clinically, and 15.4% at autopsy 2
• Adenocarcinoma: Most common histology among skin metastases cases (representing 40% of all lung cancers and frequently seen in cutaneous metastasis series) 2, 5
• Squamous cell carcinoma: Low incidence of skin metastasis 2, 4
• Small cell carcinoma: Low incidence of skin metastasis 2

Timing of Presentation

Skin metastases can present at various points in the disease course:

• 20-60% of cases: Skin lesions present before or synchronously with diagnosis of the primary lung tumor 3
• In one series: 17% presented as first manifestation, 33% found coincidentally with lung mass detection, and 50% developed after primary diagnosis 2
• Most cases (83%) occur in patients with multiple metastatic sites at the time of cutaneous involvement 5

Clinical Characteristics

Cutaneous metastases typically manifest as:

• Nodular lesions (firm, mobile or fixed, single or multiple, usually painless) ranging from 0.5-5.5 cm in diameter 3, 5, 4
• Common locations: Chest wall, back, abdomen, and extremities 5, 4
• May be ulcerated in some cases 5

Prognostic Implications

Skin metastasis from lung cancer portends an extremely poor prognosis:

• Median survival of 3.9-5 months after detection of cutaneous metastasis 1, 3, 5, 4
• Median overall survival of 10.3 months from initial lung cancer diagnosis in patients who develop skin metastases 2
• Significantly worse survival compared to advanced NSCLC without skin metastases (3.9 vs 10.0 months, P < 0.001) 1
• Almost universally associated with metastases to other organs at time of skin involvement 5, 4
• Poor response to chemotherapy, with first-line disease control rate of only 33.9% and median progression-free survival of 1.9 months 1

Clinical Pitfall

Any patient with a history of smoking or known lung cancer who develops new skin nodules should undergo biopsy to rule out cutaneous metastasis, as this finding dramatically alters prognosis and treatment planning 3. The presence of skin metastasis typically indicates stage IV disease with widespread dissemination and very limited survival 1, 5.