A Feasibility Study of Microwave Therapy for Precancerous Actinic Keratosis

D.N. Jackson; F.J. Hogarth; D. Sutherland; E.M. Holmes; P.T. Donnan; C.M. Proby

Disclosures

The British Journal of Dermatology. 2020;183(2):222-230. 

In This Article

Abstract and Introduction

Abstract

Background: Actinic keratosis (AK ) is a common premalignant skin lesion that can progress to cutaneous squamous cell carcinoma (cSCC ). Microwave therapy is an established cancer treatment and has been used for plantar viral warts.

Objectives: To evaluate the efficacy and feasibility of microwave as a treatment for AK.

Methods: Stage I was a dose-setting study, in which seven participants had the dielectric properties of 12 thick and 22 thin AK s assessed for optimization of the microwave dose used for treatment in Stage II. Stage II was a randomized, internally controlled trial evaluating 179 AK s in 11 patients (93 treated, 86 untreated controls) on the scalp/forehead or dorsal hand. Participants received one treatment initially and a repeat treatment to unresolved AK s at week 4. The response was assessed at six visits over 4 months. The primary outcome was partial or complete resolution of the treated AK s.

Results: A significantly higher proportion of treated AK areas responded than untreated (90% vs. 15%; P < 0·001). Thin AK s were more responsive than thick AK s. The site did not affect efficacy. Pain was severe, but brief (80% reported pain lasting 'a few seconds only'). Adverse effects were minimal (erythema, n = 6; flaking, n = 3; itch, n = 3). All participants who would chose microwave therapy over their current treatment cited the shorter discomfort period.

Conclusions: Microwave therapy is a portable, safe and effective treatment for AK. An easy-to-deliver, acceptable therapy for AK is attractive as a prevention strategy. While these results are promising, a larger randomized controlled trial is needed against an effective comparator to confirm clinical efficacy and patient acceptability.

Introduction

Actinic keratosis (AK) is a common precancerous skin lesion found on light-exposed sites in older fair-skinned individuals with prevalence rates of 23·5% in the Dutch population over 50 years of age.[1] AKs are precursors to cutaneous squamous cell carcinoma (cSCC), which has doubled in incidence in a decade due to ageing populations and increased ultraviolet radiation exposure.[2] The individual risk of progression to cSCC is low,[3] but 65% of cSCCs on the head and neck arise from AK.[4] A double-blind, randomized clinical trial (RCT) of 5% fluorouracil cream (5-FU) showed a 75% risk reduction for development of cSCC in the year following treatment [95% confidence interval (CI) 35–91%; P < 0·002].[5] This pivotal study suggests that annual treatment of AK should reduce the incidence of cSCC. Multiple field treatments for AK exist, such as 5-FU, imiquimod 5% cream, diclofenac 3% gel, photodynamic therapy (PDT) and lesion-directed therapy like liquid nitrogen (cryotherapy).[6] Many AK treatments require dedicated application over weeks and drive significant inflammation. Furthermore, many AK sufferers are elderly and would find compliance easier with a lesion-directed treatment.

Microwave therapies are established within oncology for ablative treatment of internal malignancies.[7,8] Microwave energy has shown promise in the treatment of recalcitrant plantar viral warts.[9] This study used a CE-marked microwave medical device (Swift® Microwave Tissue Ablation System, Emblation Ltd, Alloa, UK). The applicator of the Swift® device delivers microwave energy to the skin at a diameter up to 6 mm and depth of 2–6 mm depending on dosage. The electromagnetic waves excite water molecules, driving localized hyperthermia[10] and accelerated chemical kinetics.[11] Depending on dose, the treatment can have an ablative destructive or subablative nondestructive effect.

Here we report a first-in-human, two-stage feasibility study of microwave therapy for the treatment of AK on the bald scalp, forehead or dorsal hand.

For Stage I, the objective was to determine the dielectric properties of AK for optimization of the Swift® device microwave parameters to deliver a subablative dose of energy.

Stage II was a single-site, randomized, internally controlled trial to evaluate the efficacy, long-term resolution, safety and feasibility of microwave as a treatment.

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