Melanoma

Aspirin is one of the more interesting repurposing candidates in melanoma.

That is true for two different reasons. First, melanoma is highly immunogenic, which makes aspirin's effects on PGE2, TXA2, and immune escape especially relevant. Second, melanoma now has a real aspirin combination trial in advanced disease — and that trial taught an important lesson about dose. Read the Phase 2 paper

This is not yet a page with clear clinical proof of benefit. But it is one of the strongest pages for aspirin-immunotherapy logic.

Overview

Melanoma intersects with aspirin through three main pathways:

• COX-2 / PGE2-driven immune evasion

• platelet TXA2-mediated metastatic shielding

• possible immunotherapy potentiation

The prevention signal exists, but it is more modest than in colorectal cancer, endometrial cancer, or HCC. It also appears to be sex-specific and duration-dependent. Read the summary

The more important current story is therapeutic.

Melanoma is one of the few aspirin cancer types with a melanoma-specific Phase 2 immunotherapy-combination trial. That makes it unusually relevant for readers already on checkpoint inhibitors.

Key human data

Prevention

The prevention literature is supportive, but not fully consistent.

• A 2024 meta-analysis found that regular aspirin use was associated with lower melanoma risk, with the strongest signal in women. Read the summary

• In men, the signal trended in the same direction in some datasets, but was less consistently statistically significant. Read the summary

• As in HCC and lung cancer, duration matters. The protective signal appears stronger after 5 years or more of use. Read the summary

• Not all studies agree, and some reviews emphasise that melanoma prevention evidence remains less robust than the stronger aspirin-prevention pages. Read the commentary

So the prevention story is real enough to mention, but not strong enough to oversell.

The 2024 Phase 2 melanoma trial

This is the most important melanoma-specific aspirin study so far.

The trial enrolled 27 patients with advanced or metastatic melanoma and tested high-dose aspirin, at 1,300 mg per day, together with pembrolizumab and ipilimumab. The rationale came from strong preclinical work suggesting aspirin could improve immunotherapy response through PGE2 suppression. Read the Phase 2 paper

The main result was mixed.

The addition of high-dose aspirin did not improve outcomes clearly in the full cohort compared with what would be expected from immunotherapy alone. Toxicity was also substantially higher, especially GI toxicity. Read the Phase 2 paper

But the trial also contained the most important lesson on the page.

In the per-protocol analysis, patients who were able to stay on aspirin and complete induction showed improved survival compared with those who discontinued early. The authors concluded that the combination may still be promising, but that aspirin dose and toxicity management are critical. Read the Phase 2 paper

That creates a very specific next-step hypothesis:

high-dose aspirin was probably too toxic, and lower-dose aspirin may be the more rational combination strategy.

That low-dose hypothesis has not yet been properly tested in a melanoma trial.

The 2025 Nature mechanism and melanoma

The 2025 Nature paper on the TXA2 → ARHGEF1 → CD8-positive T-cell suppression axis used a melanoma cell line as one of its main experimental systems. That confirms the pathway is biologically active in melanoma. Read the Nature paper

An important commentary point also needs to stay visible.

Some authors have noted that the strongest validation in that study came from the lung-metastasis context, and that robust melanoma-specific clinical benefit is still unproven. Read the commentary

That is the right balance.

The mechanism is present. The clinical translation in melanoma is still incomplete.

Preclinical immunotherapy synergy

The preclinical rationale for aspirin plus immunotherapy in melanoma is strong.

Melanoma cells can produce PGE2 through COX-2, and PGE2 acts as an immune-evasion signal. It can suppress dendritic-cell function, reduce effective T-cell priming, and help create a more immunosuppressive tumour environment. Read the summary

Preclinical work from the Francis Crick Institute showed that aspirin plus immunotherapy reduced melanoma growth more than immunotherapy alone in mouse models. Read the summary

This matters because aspirin may be removing two separate immune brakes at once:

• PGE2-mediated tumour immune suppression

• TXA2-mediated platelet-supported immune evasion during metastasis

That combined logic is one of the strongest mechanistic arguments for aspirin in melanoma.

Mechanistic relevance

COX-2 and PGE2 immune evasion

Melanoma commonly upregulates COX-2 and produces PGE2.

That matters because PGE2 can:

• impair dendritic-cell maturation

• reduce effective T-cell priming

• support regulatory T-cell expansion

• weaken tumour immune infiltration

Aspirin may help by reducing this PGE2 shield. Read the summary

TXA2 and metastatic shielding

Melanoma is highly capable of haematogenous spread.

It often metastasises through the bloodstream to lung, liver, brain, and other sites. Platelet-assisted shielding of circulating melanoma cells is therefore highly relevant. Read the review

The 2025 Nature mechanism work strengthens that logic because it directly connects platelet-derived TXA2 to suppression of CD8-positive T-cell killing. Read the PubMed record

For the broader mechanism, see Aspirin and Thromboxane A2 (TXA2).

BRAF and resistance biology

About half of melanomas carry BRAF V600 mutations.

Because COX-2 / PGE2 signalling can support resistance biology more broadly, aspirin may also have relevance in BRAF inhibitor resistance. That remains a mechanistic hypothesis rather than an established clinical use case. Read the Phase 2 paper

Clinical positioning

Honest evidence assessment

Melanoma sits in a very unusual place in this section.

The biology is compelling.

The preclinical immunotherapy synergy is strong.

And unlike many pages, melanoma already has a disease-specific clinical trial.

But that trial also taught the key lesson:

dose matters enough to make or break the result.

High-dose aspirin caused enough toxicity to prevent a clean answer. That does not kill the melanoma hypothesis. It refines it. The most important open question now is whether low-dose aspirin can preserve the immunologic benefit without the same toxicity burden.

Practical interpretation

This page is especially relevant for readers with melanoma who are:

• already on pembrolizumab, nivolumab, ipilimumab, or combination checkpoint therapy

• discussing metastatic risk or recurrent disease

• known to have BRAF-mutant melanoma

The most useful questions for the treating oncology team are:

1. Am I currently on checkpoint immunotherapy, and is there any rational discussion around low-dose aspirin, not high-dose aspirin?

2. What is my BRAF status, and is resistance biology part of the treatment discussion?

3. Does the Phase 2 trial mainly teach that the combination failed, or that the dose was wrong?

4. Are platelet count, clotting history, or metastatic pattern suggesting active platelet-supported disease biology?

That is the most evidence-based way to use the melanoma aspirin literature right now.

References

• 2024 meta-analysis coverage — aspirin and melanoma prevention, strongest in women and with longer duration. Read the summary

• npj Precision Oncology 2024 — Phase 2 trial of aspirin with pembrolizumab and ipilimumab in advanced melanoma. Read the paper

• Francis Crick Institute coverage — aspirin improves immunotherapy effects in melanoma models. Read the summary

• Melanoma Research Victoria summary — COX inhibition and immunotherapy reduce melanoma growth in mice. Read the summary

• Yang et al., Nature 2025 — TXA2, ARHGEF1, and T-cell suppression, including melanoma-model relevance. Read the PubMed record

• 2025 commentary — melanoma-specific clinical evidence remains limited despite strong mechanism work. Read the commentary

• 2025 review on platelet activation, aspirin, and cancer spread. Read the review

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