Which Actinic Keratosis Treatment Works Best? Reading the Head to Head Trial

Across the four field therapies compared directly in the New England Journal of Medicine, one option separated itself from the rest. In a randomized trial of 624 patients with actinic keratosis on the head, 5 percent fluorouracil cream produced a reduction of 75 percent or more in lesions a full year after treatment in about three quarters of patients, more than double the success of the weakest arm. Compared with fluorouracil, every other treatment carried a significantly higher risk of failure. The gap was wide, and it held up under a study design built to detect exactly this kind of difference.

What the trial actually measured

The 2019 study by Jansen and colleagues enrolled patients at four Dutch hospitals between November 2014 and March 2017. Each participant had at least five actinic keratosis lesions within one continuous area of 25 to 100 square centimeters on the head, and each was randomly assigned to one of four field-directed treatments: 5 percent fluorouracil cream, 5 percent imiquimod cream, methyl aminolevulinate photodynamic therapy (MAL-PDT), or 0.015 percent ingenol mebutate gel.

The primary outcome was the proportion of patients who reached a 75 percent or greater reduction in lesion count, measured from baseline to 12 months after treatment ended. That 12-month horizon is the quiet strength of the design. Many actinic keratosis studies report clearance a few weeks after treatment, when almost any therapy that inflames and peels the skin looks impressive. Waiting a year separates durable clearance from a cosmetic flush that fades.

By that stricter yardstick, the arms diverged sharply. Fluorouracil succeeded in 74.7 percent of patients (95 percent confidence interval, 66.8 to 81.0). Imiquimod reached 53.9 percent, MAL-PDT 37.7 percent, and ingenol mebutate 28.9 percent. The ranking is not a photo finish. The best-performing arm cleared roughly two and a half times as many patients as the worst.

Reading the hazard ratios

The authors summarized the comparisons as hazard ratios for treatment failure, each measured against fluorouracil as the reference. A hazard ratio describes relative risk over the follow-up period: a value of 1.0 would mean no difference from fluorouracil, and higher numbers mean failure came more often or sooner.

Against fluorouracil, the hazard ratio for treatment failure was 2.03 with imiquimod (95 percent confidence interval, 1.36 to 3.04), 2.73 with MAL-PDT (1.87 to 3.99), and 3.33 with ingenol mebutate (2.29 to 4.85). In plain terms, patients treated with ingenol mebutate were more than three times as likely to reach the failure endpoint as those treated with fluorouracil. Two features make these numbers persuasive rather than noisy. Every confidence interval sits entirely above 1.0, so none of the differences is compatible with equivalence, and each comparison carried a P value at or below 0.001. This is a case where the effect size and the statistical certainty point the same direction.

One honest caveat belongs here. Fluorouracil's edge came with a cost in tolerability. It tends to produce more intense local skin reactions during the treatment course, including redness, crusting, and irritation. The trial's headline measure was durable effectiveness at one year, and that tolerability trade-off is part of any real appraisal.

Why field cancerization is the right target

The logic behind treating a whole zone of skin rather than dabbing individual spots rests on a concept called field cancerization. Chronic ultraviolet exposure does not damage keratinocytes one lesion at a time. It alters a broad territory of skin, seeding genetic changes across cells that still look normal to the eye. The visible actinic keratosis is the tip of that reservoir, and clinically silent lesions sit alongside it.

Freezing or scraping the lesions you can see, known as lesion-directed treatment, leaves that surrounding field intact, which is why new lesions so often surface nearby. Field therapy applies a treatment across the entire affected area to reach subclinical damage as well. That is the rationale the trial was built to test, and it explains why the outcome was measured across a defined patch of skin rather than lesion by lesion.

The ingenol mebutate footnote

The trial carries a postscript that sharpens its message. Ingenol mebutate, the weakest of the four arms, no longer exists as an approved product in Europe. In early 2020 the European Medicines Agency reviewed its safety after data pointed to a higher number of skin cancers in treated areas. The agency concluded in April 2020 that the risks outweighed the benefits, citing an increased occurrence of skin cancer, particularly squamous cell carcinoma, compared with imiquimod-treated skin. The marketing authorization had already been suspended and then withdrawn earlier that year.

So the arm that performed worst on durable clearance also turned out to carry the least favorable safety profile. It is a useful reminder that the regimen marketed as the quickest and most convenient is not automatically the one that serves a patient best over time.

What the evidence supports, and what it does not

Read carefully, this trial makes a specific claim: among these four field therapies, at these formulations and strengths, for multiple actinic keratoses on the head, fluorouracil delivered the most durable clearance at one year. It does not crown a treatment for every anatomic site, every lesion grade, or every patient who cannot tolerate a demanding topical course. A single well-run trial is strong evidence, not the whole literature, and body-site differences, cost, and tolerability all shape real decisions.

What the data do offer is a clear reference point. When one arm doubles the durable response of another and the confidence intervals never overlap the line of no effect, the signal is worth taking seriously. This article is educational and not medical advice; anyone weighing treatment for sun-damaged skin should have that conversation with a qualified clinician who can examine the lesions directly.