Cutaneous squamous cell carcinoma (SCC) spreads in roughly 2 to 5 percent of cases overall, making it far less aggressive than many internal cancers but considerably more dangerous than its reputation as “just a skin cancer” suggests. That range depends heavily on where the tumor sits, how deep it grows, and the patient’s immune status. A nationwide registry study found a cumulative metastasis rate of about 1.9 percent over ten years, while other research places the figure higher, and certain subgroups face risks many times the average.
What the Overall Numbers Look Like
The commonly cited range for cutaneous SCC metastasis is about 1.2 to 5 percent, though researchers have increasingly noted this spread may be more concerning than older estimates implied.1PubMed. The risk of metastases from squamous cell carcinoma of the skin A large Dutch cancer registry study tracking thousands of patients found a cumulative metastasis incidence of 1.9 percent after ten years, with a median time from first SCC diagnosis to metastasis of about a year and a half.2Journal of the American Academy of Dermatology. Cumulative incidence and disease-specific survival of metastatic cutaneous squamous cell carcinoma: A nationwide cancer registry study A separate cohort study calculated a mean annual metastasis rate of 2.28 percent among primary SCCs.3PubMed Central. Risk Factors and Prognosis for Metastatic Cutaneous Squamous Cell Carcinoma: A Cohort Study
Those single-digit percentages may not sound alarming, but SCC is extraordinarily common. It is one of the most frequently diagnosed cancers in the world. Even a small percentage of a very large number translates to a substantial number of people developing metastatic disease each year. A prospective study following over 600 patients for a median of about 43 months saw 4 percent develop metastases during follow-up.4The Lancet Oncology. Analysis of risk factors determining prognosis of cutaneous squamous-cell carcinoma: a prospective study The variance between studies partly reflects differences in which patients are being counted: a study from a referral center seeing more complex tumors will naturally report a higher rate than a population-wide registry that includes every thin, low-risk SCC.
Where the Tumor Sits on Your Body
Not all skin is created equal when it comes to SCC spread. Tumors on the ear, lip, and scalp are among the most dangerous. One study directly compared sites and found that SCC on the scalp, ear, and lip metastasized about 9 percent of the time, while SCC on the lower leg showed a 0 percent metastasis rate in the same cohort.5Journal of the American Academy of Dermatology. The scalp is a high-risk site for cutaneous squamous cell carcinoma metastasis Even after controlling for tumor depth, patient age, sex, and immune status, scalp location remained an independent risk factor for spread, performing similarly to the ear and lip.
The face, genitalia, hands, and feet are also considered high-risk zones.6PubMed. Cutaneous Squamous Cell Carcinoma: A Review of High-Risk and Metastatic Disease The ear specifically carried a hazard for metastasis roughly three and a half times higher than lower-risk sites in a multivariate analysis.7Journal of the American Academy of Dermatology. Prognostic factors for local recurrence, metastasis, and survival rates in squamous cell carcinoma of the skin, ear, and lip The likely explanation involves the thinner soft tissue and rich lymphatic and nerve supply in these areas, giving tumor cells easier access to drainage pathways.
Tumor Features That Raise the Odds
Beyond location, a handful of features visible under the microscope drive much of the risk. Depth of invasion is the single most consistent predictor. Tumors that grow deeper than about 2 millimeters are classified as high-risk, and the relationship between thickness and metastasis holds up across multiple studies and cancer types.6PubMed. Cutaneous Squamous Cell Carcinoma: A Review of High-Risk and Metastatic Disease One multivariate analysis found that increased tumor thickness carried a hazard nearly five times higher for metastasis, making it the strongest individual predictor in that dataset.7Journal of the American Academy of Dermatology. Prognostic factors for local recurrence, metastasis, and survival rates in squamous cell carcinoma of the skin, ear, and lip Wider tumors also matter: horizontal size above 20 millimeters is independently associated with worse outcomes.
Perineural invasion, where tumor cells grow along nerve sheaths, is another red flag. A prospective study of nearly 1,400 tumors found that SCC with perineural invasion had substantially higher rates of lymph node metastasis, local recurrence, and tumor-specific death compared with tumors without it. When perineural invasion combined with a particular aggressive growth pattern called desmoplasia, death rates climbed sharply: tumor-specific death reached 54 percent for desmoplastic SCC with perineural invasion, compared to 4 percent for standard SCC without either feature.8PubMed. Prognostic Impact of Perineural Invasion in Cutaneous Squamous Cell Carcinoma: Results of a Prospective Study of 1,399 Tumors Poor histological differentiation, meaning the tumor cells look very abnormal under a microscope, also bumps up the risk.
Immunosuppression Changes Everything
People with weakened immune systems face a fundamentally different version of this disease. Organ transplant recipients, who take medications to prevent rejection that also suppress the immune system’s cancer surveillance, develop SCC far more often and with a more aggressive course.9PubMed Central. Aggressive Squamous Cell Carcinoma in Organ Transplant Recipients A prospective multicenter European study of over 500 transplant patients found that the cumulative metastasis incidence reached about 4.5 percent at just one year and 6.2 percent at two years after SCC diagnosis.10Journal of the American Academy of Dermatology. Cumulative incidence and risk factors for cutaneous squamous cell carcinoma metastases in organ transplant recipients Compare that to the roughly 1.9 percent at ten years in the general population, and you can see the magnitude of the difference.
Immunosuppression also showed up as an independent risk factor in multivariate analyses of the general population, roughly quadrupling the hazard of metastasis even when tumor size, location, and thickness were accounted for.7Journal of the American Academy of Dermatology. Prognostic factors for local recurrence, metastasis, and survival rates in squamous cell carcinoma of the skin, ear, and lip This applies not only to transplant recipients but also to people on immunosuppressive therapy for autoimmune conditions, those with chronic lymphocytic leukemia, and people living with HIV. If you are in any of these groups and develop an SCC, your dermatologist will typically treat it with narrower margins and closer follow-up than for an otherwise healthy patient.
Burn Scar SCC and Mucosal SCC Are Outliers
Two subcategories of SCC behave so differently from typical sun-induced skin SCC that they deserve separate attention. SCC that arises within chronic burn scars, sometimes called Marjolin ulcers, has been reported to metastasize at rates around 30 percent, roughly ten times higher than standard cutaneous SCC.11Burns Open. Co-existence of basal cell carcinoma and squamous cell carcinoma in a single burn scar region These tumors tend to develop in areas of chronic scarring and inflammation where the normal skin architecture has been replaced, and they are often diagnosed late because changes in scar tissue can be subtle.
SCC of mucosal surfaces, such as the inside of the mouth, behaves more like a head and neck cancer than a skin cancer. Mucosal SCC carries significantly higher rates of lymph node involvement and worse survival than its cutaneous counterpart on the lip.12PubMed. Squamous Cell Carcinoma of the Lip-A Review of Squamous Cell Carcinogenesis of the Mucosal and Cutaneous Junction When you hear statistics about SCC spread, it is important to know whether the numbers refer to cutaneous (skin) SCC or mucosal/head-and-neck SCC, because the two are almost separate diseases in terms of prognosis.
How Recurrence and Local Spread Lead to Death
Metastasis to distant organs is not the only way SCC kills. A study of 1,400 patients found that about 9 percent developed either local recurrence, locoregional metastasis (spread to nearby lymph nodes), or both. Among those who developed locoregional metastasis alone, about a third died of their disease. When both local recurrence and locoregional metastasis occurred together, the death rate climbed to 64 percent. Overall, SCC-specific death occurred in 2.4 percent of the full cohort, with a median time from recurrence or metastasis to death of about 1.3 years.13PubMed Central / Wiley Online Library. Local recurrence and locoregional metastases as precursors of death by cutaneous squamous cell carcinoma
This underscores a point that sometimes gets lost in discussions focused on distant metastasis: even regional spread to nearby lymph nodes can be lethal. The transition from a localized tumor to one that has reached the regional nodes is the most consequential event in determining whether a patient survives, more so than the jump from regional nodes to distant organs.
How Doctors Look for Spread
For high-risk SCCs, sentinel lymph node biopsy has been investigated as a way to catch early nodal spread. A literature review covering 130 cases found that the sentinel node was positive for cancer in about 14 percent of high-risk SCCs overall, with positivity rates of roughly 10 percent for head and neck tumors and nearly 19 percent for those on the trunk or extremities.14PubMed Central. Sentinel lymph node biopsy for high-risk cutaneous squamous cell carcinoma: clinical experience and review of literature A separate study of head and neck SCCs found a positivity rate around 11 to 15 percent after more thorough tissue processing.15PubMed. Sentinel Lymph Node Biopsy for Cutaneous Squamous Cell Carcinoma on the Head and Neck Sentinel node biopsy remains somewhat controversial for SCC because it is not yet clear that catching early nodal disease this way improves survival, unlike in melanoma where it has become standard practice.
Imaging plays a role when high-risk features or clinical suspicion of spread exist. A systematic review found that CT scanning showed the highest sensitivity for detecting nodal metastasis among cutaneous SCCs, at over 96 percent, and that imaging changed clinical management in up to a third of cases.16PubMed. Use of Imaging in Cutaneous Squamous Cell Carcinoma to Detect High-Risk Tumor Features, Nodal Metastasis, and Distant Metastasis: A Systematic Review MRI was particularly good at identifying perineural spread, with a sensitivity around 95 percent. PET-CT scans can pick up disease that conventional imaging misses: in one study of high-risk cutaneous SCCs, PET-CT detected previously unknown metastatic lesions in about a fifth of patients and changed management accordingly.17PubMed Central. Clinical value of FDG-PET/CT in staging cutaneous squamous cell carcinoma
Where SCC Tends to Spread
When head and neck SCC does develop distant metastases, the lungs are the most common destination, accounting for roughly 70 percent of cases. Bone and liver are the next most frequent sites.18PubMed. Distant metastases from head and neck squamous cell carcinoma. Part I. Basic aspects About half of distant metastases from head and neck SCC are detected within nine months of treatment, and 80 percent within two years, which is why the first two years of follow-up after treating a high-risk SCC are the most intensive.19PubMed Central. Tumor Biomarkers for the Prediction of Distant Metastasis in Head and Neck Squamous Cell Carcinoma
One particularly sobering finding from autopsy studies is that distant metastases are found in roughly a quarter to over 40 percent of head and neck SCC patients who were originally staged as having no lymph node involvement.19PubMed Central. Tumor Biomarkers for the Prediction of Distant Metastasis in Head and Neck Squamous Cell Carcinoma This suggests that current staging methods, even with modern imaging, still miss a meaningful fraction of spread. The clinical implication is that a clean set of scans after treatment does not guarantee the cancer is gone, which is why ongoing surveillance matters.
How Staging Systems Estimate Your Risk
Two main classification systems help doctors estimate the likelihood of spread for a given tumor. The AJCC (American Joint Committee on Cancer) 8th edition system and the Brigham and Women’s Hospital (BWH) system both assign tumors a stage based on features like size, depth, perineural invasion, and bone involvement. A head-to-head comparison found that both performed similarly for predicting local recurrence, but the BWH system was significantly better at predicting nodal metastasis and disease-specific death.20JAMA Dermatology. Performance of the American Joint Committee on Cancer Staging Manual, 8th Edition vs the Brigham and Women’s Hospital Tumor Classification System for Cutaneous Squamous Cell Carcinoma
In immunosuppressed patients specifically, the staging systems showed a steep risk gradient. Under the AJCC system, the risk of a poor outcome (metastasis, disease-specific death, or both) was under 2 percent for T1 tumors but jumped to over 36 percent for T3 tumors. The BWH system showed a similar jump, from under 2 percent for T1 to 100 percent for T3.21PubMed. Stratification of Poor Outcomes for Cutaneous Squamous Cell Carcinoma in Immunosuppressed Patients Using the American Joint Committee on Cancer Eighth Edition and Brigham and Women’s Hospital Staging Systems The practical takeaway is that early-stage SCC in immunosuppressed patients is still relatively manageable, but once it reaches higher stages, the prognosis deteriorates dramatically. That makes early detection through routine skin examinations even more critical for this population.
Treatment When SCC Has Already Spread
For years, metastatic cutaneous SCC had limited treatment options beyond surgery and radiation. That changed with the approval of cemiplimab, an immunotherapy drug that blocks PD-1, a protein some cancers exploit to hide from the immune system. In the pivotal phase 2 trial, about 47 percent of patients with metastatic cutaneous SCC responded to cemiplimab, including both partial and complete tumor shrinkage.22New England Journal of Medicine. PD-1 Blockade with Cemiplimab in Advanced Cutaneous Squamous-Cell Carcinoma A combined analysis of additional trial groups showed an overall response rate around 45 percent, with responses that tended to be durable, meaning the tumors stayed shrunken for months or longer in most responders.23PubMed Central. Phase 2 study of cemiplimab in patients with metastatic cutaneous squamous cell carcinoma: primary analysis of fixed-dosing, long-term outcome of weight-based dosing
Extended follow-up data showed that the estimated probability of being alive at two years was about 73 percent for patients treated with cemiplimab, with the median overall survival not yet reached at the time of analysis, meaning more than half the patients were still alive when the data was last reviewed.24PubMed Central. Integrated analysis of a phase 2 study of cemiplimab in advanced cutaneous squamous cell carcinoma: extended follow-up of outcomes and quality of life analysis Before immunotherapy, metastatic cutaneous SCC was often treated with platinum-based chemotherapy that had modest response rates and significant side effects. Cemiplimab represented a genuine shift in what is possible for patients with advanced disease, though it does not work for everyone and carries its own immune-related side effects.
From Precursor Lesion to Cancer
Many SCCs begin as actinic keratoses, those rough, scaly patches that develop on sun-exposed skin over decades. The risk that any individual actinic keratosis will progress to invasive SCC is low, with published estimates ranging from about 0.025 percent to 16 percent per year depending on the study population and methods. An aggregation of these studies suggested an average progression rate of about 8 percent.25PubMed. The risk of progression to invasive disease The trouble is that many people have dozens or even hundreds of actinic keratoses, so even a low per-lesion risk can add up. It remains impossible to predict which specific spots will turn malignant, which is why dermatologists often recommend treating them broadly rather than watching and waiting.
This progression from precursor to invasive cancer to potential metastasis is a reminder that the numbers discussed throughout this article represent a cascade. Most actinic keratoses never become SCC. Most SCCs never spread. But the ones that do spread tend to share the high-risk features described earlier: deep invasion, high-risk location, immunosuppression, or perineural involvement. Catching SCC while it is still thin and localized is the single most effective way to keep yourself on the favorable side of the statistics.