How Often Does Squamous Cell Carcinoma Spread?

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.¹ 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.² A separate cohort study calculated a mean annual metastasis rate of 2.28 percent among primary SCCs.³

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.⁴ 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.⁵ 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.⁶ The ear specifically carried a hazard for metastasis roughly three and a half times higher than lower-risk sites in a multivariate analysis.⁷ 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.⁶ 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.⁷ 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.⁸ 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.⁹ 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.¹⁰ 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.⁷ 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.¹¹ 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.¹² 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.¹³

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.¹⁴ A separate study of head and neck SCCs found a positivity rate around 11 to 15 percent after more thorough tissue processing.¹⁵ 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.¹⁶ 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.¹⁷

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.¹⁸ 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.¹⁹

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.¹⁹ 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.²⁰

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 T3.²¹ 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.²² 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.²³

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.²⁴ 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.²⁵ 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.