Does Skin Cancer Show Up in Blood Work?

A standard blood panel ordered at your annual checkup will not detect skin cancer. No routine complete blood count or metabolic panel is designed to flag melanoma, squamous cell carcinoma, or basal cell carcinoma. That said, specific blood-based biomarkers do exist for certain skin cancers, and some newer tests are moving closer to clinical use. The gap between what routine blood work can do and what specialized blood-based tests can do is wider than most people realize, and understanding where that line falls matters if you or someone you know is dealing with a skin cancer diagnosis.

What Routine Blood Work Actually Measures

When your doctor orders “blood work,” they typically mean a complete blood count and a basic or comprehensive metabolic panel. These tests look at things like red and white blood cell counts, hemoglobin, kidney function markers, liver enzymes, electrolytes, and blood sugar. None of these values are specific to skin cancer. A person with early-stage melanoma will almost always have perfectly normal results on these standard panels.

That does not mean blood work is irrelevant once skin cancer is in the picture. Some of the values on a routine panel can shift in advanced disease or during treatment. But the shift is a consequence of cancer’s systemic effects, not a direct signal of the cancer itself. Thinking of routine blood work as a skin cancer screening tool will lead you astray.

LDH and S100B in Melanoma

Two blood markers have a long track record in melanoma care: lactate dehydrogenase (LDH) and S100B protein. Neither is used to diagnose melanoma in the first place. Both are used after diagnosis to gauge prognosis and monitor disease progression, especially in advanced stages.

LDH is an enzyme found in many tissues, and its levels rise when cells are damaged or dying rapidly, which happens more in aggressive cancers. A large meta-analysis of melanoma patients receiving immunotherapy found that elevated LDH before treatment roughly doubled the risk of shorter survival and was linked to faster disease progression.¹ Separate work found that for each increase of 100 IU/L in baseline LDH, the risk of death rose meaningfully, and LDH was moderately accurate at predicting survival outcomes months out.² LDH is included in the staging criteria for stage IV melanoma for good reason. But it is not specific to melanoma. Your LDH can spike from intense exercise, liver disease, heart problems, or an infection. It is a red flag in context, not a standalone alarm.

S100B is more melanoma-specific. It is a protein released by melanoma cells, and rising levels after surgery tend to predict relapse. In a large study of surgically resected high-risk melanoma patients, higher baseline S100B was a significant prognostic factor for survival even after adjusting for ulceration, lymph node involvement, and treatment. Patients whose S100B started low and then climbed during follow-up had some of the worst outcomes.³ S100B is used more widely in European melanoma guidelines than in the United States, where many oncologists rely on imaging and LDH instead.

A real limitation of S100B is that it produces false positives. Conditions like obesity, liver cirrhosis, chronic kidney disease, migraine, and prior stroke have all been associated with elevated S100B in people who do not have melanoma.⁴ So a high reading demands further investigation rather than immediate panic.

Circulating Tumor DNA and Liquid Biopsies

The most exciting developments in blood-based cancer detection involve what are broadly called liquid biopsies. Instead of measuring a generic protein like LDH, liquid biopsies look for fragments of tumor DNA (ctDNA) or actual cancer cells floating in the bloodstream. For melanoma specifically, this technology has moved from pure research into early clinical use.

The basic idea is straightforward. Tumors constantly shed tiny fragments of their DNA into the blood. If you know what mutations the tumor carries, you can design a test to look for those specific mutations in a blood draw. In melanoma, BRAF mutations are among the most common targets. One study found roughly 90% concordance between the mutations identified in tumor tissue and those detected in plasma, and ctDNA levels tracked with clinical disease course about 96% of the time. The study also found that rising ctDNA preceded relapse detected by imaging and was more specific than either S100B or LDH for that purpose.⁵

For patients who have had melanoma surgically removed, ctDNA can help predict who is at high risk of relapse. In a study of stage III BRAF-mutant melanoma patients starting adjuvant therapy, about a third had detectable ctDNA at baseline. Those patients had dramatically worse outcomes: three-year overall survival was around 55% compared with 95% in the ctDNA-negative group. Among the high-risk patients, those who cleared their ctDNA during treatment did not relapse, while persistent ctDNA gave early warning of recurrence.⁶ An independent study confirmed these patterns, finding that ctDNA detection after surgery predicted relapse with a hazard ratio of 10 and that the result held up after adjusting for disease stage and mutation status.⁷

Personalized ctDNA assays are getting more refined. In high-risk melanoma, patients with detectable ctDNA at their first post-surgical blood draw had a significantly shorter overall survival compared to those whose blood was clear of tumor DNA, with a hazard ratio above 6.⁸ These results are reshaping how doctors think about follow-up after melanoma surgery. Rather than relying solely on scheduled scans, blood-based monitoring might flag recurrence months earlier.

Where ctDNA Falls Short

The enthusiasm for liquid biopsies needs to be tempered by a clear-eyed look at what they cannot yet do. ctDNA is not a reliable screening tool for finding skin cancer you do not already know about, especially early-stage disease.

The core issue is sensitivity. When the tumor is small or localized, it sheds relatively little DNA into the bloodstream. One study found circulating tumor cells in only about 29% of patients with primary invasive melanoma, compared with roughly 63% of patients with metastatic disease.⁹ A separate analysis of concordance between tissue and plasma found that the match was best in patients with a high disease burden, meaning larger tumors, multiple metastatic sites, or already-elevated LDH. In radically resected stage III and IV patients with no visible disease remaining, ctDNA sensitivity was too low to reliably predict relapses.¹⁰

A recent retrospective study looking specifically at melanoma patients who had a negative ctDNA result before confirmed recurrence found that the overall sensitivity of a commercially available ctDNA assay for detecting relapse was only about 54%.¹¹ In other words, roughly half of melanoma recurrences were missed. That is enough to be useful alongside other monitoring tools, but it means a clean ctDNA result is not a guarantee that you are in the clear.

Non-Melanoma Skin Cancers and Blood Markers

Most conversations about blood-based detection focus on melanoma because it is the deadliest common skin cancer and the one most likely to spread internally. But basal cell carcinoma and cutaneous squamous cell carcinoma, which together account for the vast majority of skin cancer diagnoses, are even harder to detect through blood tests. These cancers tend to stay localized, grow slowly, and shed very little material into the bloodstream. There is no established blood biomarker for routine basal cell or squamous cell carcinoma.

Merkel cell carcinoma is an exception worth knowing about. This rare but aggressive skin cancer is often caused by Merkel cell polyomavirus, and the virus triggers a measurable antibody response. About half of Merkel cell carcinoma patients have detectable antibodies to the virus’s oncoprotein at diagnosis. Among those who were seropositive, falling antibody titers after treatment tracked with disease clearance, while rising titers had a positive predictive value of 66% for recurrence. Perhaps more useful, a decreasing titer had a negative predictive value of 97%, meaning a dropping number was a very reliable sign that the cancer was not coming back.¹² A separate study confirmed that seropositivity improved survival outcomes, though the benefit was clearest in patients with localized disease at presentation.¹³ This makes the antibody test one of the most actionable blood markers available for any skin cancer, and clinicians are increasingly using it in Merkel cell carcinoma surveillance.¹⁴

The Neutrophil-to-Lymphocyte Ratio

One surprisingly simple blood marker that keeps showing up in melanoma research is the neutrophil-to-lymphocyte ratio, or NLR. You already have the numbers on any standard complete blood count: it is just the count of neutrophils divided by the count of lymphocytes. No special test is needed.

A pooled analysis of melanoma patients receiving immunotherapy found that a higher baseline NLR was associated with roughly two and a half times the risk of shorter overall survival and progression-free survival. The pattern held across different types of immunotherapy and across different study designs.¹⁵ Elevated NLR has also been correlated with worse outcomes in localized high-risk melanoma treated with surgery alone.¹⁶

NLR is not melanoma-specific at all. Infections, stress, and inflammatory conditions all raise it. But as a cheap, always-available number that adds prognostic information, it has real value for doctors managing melanoma cases. If you are being treated for melanoma and your oncologist mentions your NLR, this is why.

When Skin Cancer Indirectly Alters Blood Work

There is one situation in which skin cancer can cause genuinely abnormal results on a standard blood panel, and it has nothing to do with tumor DNA or specific biomarkers. Advanced cutaneous squamous cell carcinoma can trigger paraneoplastic syndromes, where the tumor secretes hormones or proteins that disrupt the body’s normal chemistry.

The most commonly reported paraneoplastic effect in keratinocyte skin cancers is malignancy-associated hypercalcemia. In a systematic review, it accounted for about 78% of all reported paraneoplastic cases, and the vast majority were linked to squamous cell carcinoma rather than basal cell carcinoma. The hypercalcemia was severe in about 60% of cases. The mechanism usually involves the tumor producing parathyroid hormone-related protein, which drives calcium levels up.¹⁷ In some patients, this is accompanied by an abnormally high white blood cell count.¹⁸

These cases are rare and usually involve large, aggressive, or neglected tumors. But if a patient shows up with unexplained high calcium, a non-healing skin lesion, and an elevated white count, that combination should raise suspicion. It is one of the few scenarios where standard blood work genuinely points toward skin cancer, even though the abnormality is an indirect effect rather than a direct marker.

Research-Stage Technologies

Several newer approaches are in earlier stages of development and not yet part of clinical practice, but they hint at where blood-based skin cancer detection is headed.

Autoantibody panels represent one approach. The immune system sometimes produces antibodies against proteins expressed by tumor cells. Researchers screened hundreds of blood samples from melanoma patients and healthy volunteers against a microarray of over 1,600 proteins and identified a combination of 10 autoantibody markers that, as a group, detected primary melanoma with about 79% sensitivity and 84% specificity.¹⁹ Those numbers are nowhere near good enough for population-wide screening, but they are encouraging for a first-pass study on primary (early) melanomas rather than advanced disease.

Metabolomics is another frontier. A pilot study using high-resolution mass spectrometry compared serum metabolite profiles of melanoma patients and healthy controls. The researchers identified several lipid metabolites that differed between the groups and built a classification model using three of them that achieved about 94% accuracy when validated on an independent set of stage I melanoma patients.²⁰ These are very small sample sizes, and pilot results routinely shrink when tested in larger, more diverse populations. But the concept of profiling blood chemistry to catch melanoma before it becomes advanced has obvious appeal.

Exosome-derived microRNAs have also drawn attention. Tumor cells release tiny vesicles called exosomes that carry RNA fragments, and the microRNA signatures inside those vesicles differ between melanoma patients and healthy controls.²¹ None of these microRNA-based approaches are ready for clinical use, but they represent yet another angle for extracting cancer signals from blood.

Circulating tumor cells themselves can also be captured. A melanoma-specific microsystem detected melanoma cells in the blood of patients across all stages, and the number of cells dropped significantly after surgical removal of the tumor.²² The practical challenge is that these cells are extremely rare in early-stage disease, and the technologies to reliably find them remain expensive and technically demanding.

Multi-Cancer Early Detection Tests

You may have seen advertising for blood tests marketed as multi-cancer early detection (MCED) screens. These tests, the best known being Galleri, analyze patterns in cell-free DNA to flag a range of cancers from a single blood draw. Skin cancer does appear on the list of cancer types these tests aim to detect, but the picture is more complicated than the marketing suggests.

The available data on MCED test performance for skin cancer specifically is thin. In one assessment of test sensitivity across cancer types, only a handful of non-melanoma non-basal cell carcinoma/squamous cell carcinoma skin cancer cases were even included in the analysis.²³ With sample sizes that small, it is impossible to draw conclusions about how well these tests work for skin cancer as a category. Common basal and squamous cell carcinomas, which are overwhelmingly the most frequent skin cancers, shed so little material into the blood that a blood-based screen faces a fundamental biological challenge with them. For melanoma, the detection problem is different: melanoma does shed DNA into the blood, but early-stage melanomas are small and their signal may fall below the test’s detection threshold.

The bottom line for anyone considering one of these tests is that they are not a substitute for skin checks. A dermatologist looking at your skin with a dermatoscope remains far more sensitive for catching early skin cancer than any blood test currently available. If you have risk factors for melanoma, regular full-body skin exams remain the evidence-based approach to early detection, and that is unlikely to change anytime soon. Blood-based tools are making real headway in monitoring known melanoma, predicting recurrence, and guiding treatment, but the era of a simple blood draw replacing a thorough skin exam has not arrived.