Incidence of Metastatic Skin Cancer
The incidence of metastatic skin cancer varies substantially by tumor type: cutaneous squamous cell carcinoma (cSCC) metastasizes in 1.2-5% of cases, basal cell carcinoma (BCC) rarely metastasizes (extremely rare, <0.1%), and Merkel cell carcinoma (MCC) shows regional or distant metastasis in 52-59% and 34-36% of cases respectively. 1, 2, 3
Squamous Cell Carcinoma Metastatic Rates
The overall metastatic rate for cSCC ranges from 1.2% to 5% in the general population, with significant variation based on risk factors 1, 2, 4. A large UK population-based study of 1,495 tumors found a metastatic rate of only 1.2%, suggesting that real-world rates may be lower than previously reported 1.
Risk-Stratified Metastatic Rates for cSCC:
- Low-risk tumors (sun-exposed sites, <2 cm, well-differentiated): Metastatic rate approximately 9.1% 3
- High-risk tumors (>2 cm diameter): Metastatic rate approximately 30.3% 3
- Deep tumors (>4 mm depth or Clark level V): Metastatic rate 45.7% 3
- Superficial tumors (<4 mm depth, upper dermis): Metastatic rate 6.7% 3
- Immunosuppressed patients (organ transplant recipients): Significantly higher metastatic rates, though exact percentages vary 3
Timing of Metastasis:
Approximately 70-80% of all cSCC metastases develop within 2 years of initial diagnosis, making this the critical surveillance window 3, 1.
Basal Cell Carcinoma Metastatic Rates
BCC metastasis is exceedingly rare, occurring in far less than 1% of cases 3. The disease characteristically demonstrates indolent local behavior with minimal metastatic potential 3. Even in immunosuppressed individuals, few published data suggest increased metastatic risk for BCC 3.
Merkel Cell Carcinoma Metastatic Rates
MCC is highly aggressive with documented rates of regional disease in 52-59% of cases and distant metastatic disease in 34-36% 3. Local recurrence develops in 25-30% of all MCC cases 3. This tumor combines the local recurrence rates of infiltrative non-melanoma skin cancer with the regional and distant metastatic rates of thick melanoma 3.
Recurrence Rates
Local recurrence rates for cSCC vary by tumor size and location:
- Tumors >2 cm: Local recurrence rate 15.2% 3
- Tumors <2 cm: Local recurrence rate 7.4% 3
- High-risk anatomic sites (mask areas of face, ≥6 mm): Significantly higher recurrence rates 3
- Middle-risk sites (≥10 mm): Elevated recurrence rates 3
Critical Risk Factors That Increase Metastatic Potential
Anatomic Location:
Site significantly influences metastatic risk, with ear and lip locations showing higher rates than sun-exposed trunk sites 3. The hand is considered a high-risk anatomical location 5.
Perineural Invasion:
Perineural involvement greatly increases both recurrence and metastatic risk for cSCC 3. This finding warrants aggressive management and close surveillance 3.
Immunosuppression:
Organ transplant recipients have significantly greater metastatic rates compared to immunocompetent patients 3. The metastatic rate increases 2-3 times higher in immunosuppressed patients 5.
Tumor Differentiation:
Poorly differentiated tumors carry substantially higher metastatic risk than well-differentiated lesions 3, 6.
Mortality Implications
When metastasis occurs, mortality rates exceed 70% in several large studies of metastatic cSCC 4. MCC has a mortality rate that exceeds melanoma, with overall 5-year survival rates ranging from 30-64% 3.
Common Pitfalls to Avoid
Do not assume all cSCC carries the same metastatic risk—stratification by size, depth, location, differentiation, and immunosuppression status is essential for appropriate surveillance planning 3, 4.
Do not overlook the 2-year window—the vast majority of metastases declare themselves within 24 months, requiring intensive surveillance during this period 3, 1.
Do not equate BCC and cSCC metastatic potential—BCC metastasis is extraordinarily rare while cSCC carries meaningful metastatic risk requiring different management approaches 3.