Plantar warts are common among the general population. After failure of first-line treatment, they are challenging to treat.

To compare 4 second-line treatments — 50 % salicylic acid ointment (SA) under occlusion, liquid nitrogen, 5 % 5-fluorouracil (5-FU) cream under occlusion, and 5 % imiquimod cream — in terms of complete remission after 90 days.

A multicentre, pragmatic, randomized, controlled trial. Screened patients with plantar warts were initially treated with a 5-week regimen of SA, followed by a 1-week washout period. Patients exhibiting treatment failure were randomly assigned to one of five treatments, with the allocation ratio fixed at 1:1:1:1:1. The fifth arm, treated with duct tape, was withdrawn during the study. We aimed to enrol 436 patients (109 in each treatment), but based on an anticipated response rate of 33 % in the pre-inclusion period, the target enrolment figure was increased to 660. An ancillary study (BIOVRAIE) was planned to analyse wart genotypes. The trial was registered on ClinicalTrials.gov (NCT 01059110).

A total of 358 patients (54 % of the target) were enrolled in the pre-inclusion period; 140 patients achieved complete remission during this period and 174 were included. Myrmecia warts constituted the most prevalent form of plantar warts (83.9 %), followed by mosaic warts (13.2 %) and a combination of both (2.8 %). Human papilloma virus (HPV) 27 and HPV1 infection were predominant (90 % and 84 %, respectively). At inclusion, 22 patients were assigned to the duct tape arm before its withdrawal, 41 to SA, 36 to cryotherapy, 33 to 5-FU, and 42 to imiquimod. On Day 90, 6 (20 %) patients in the SA group were in complete remission, as well as 3 (11 %) in the cryotherapy group, 1 (3.5 %) in the 5-FU group, 2 (6.6 %) in the imiquimod group.

While the trial failed to enrol the planned number of patients, the study showed that no treatment had a substantial positive effect as second-line treatment of plantar warts.

# Introduction

Cutaneous viral warts are common and are caused by human papilloma virus (HPV) infection. Two large population studies across all age groups in the United States and Russia produced markedly different prevalence rates for viral warts: 0.84 % and 12.9 %, respectively [1,2]. Among immunocompetent individuals, non-genital warts are usually harmless and spontaneously resolve within months to years [3]. Cutaneous warts represent a significant cost for health insurance. Data from the United Kingdom showed that general practioners treat cutaneous (non-genital) warts in 2 million patients each year [4]. With each treatment prescribed in general practice in the United Kingdom costing the National Health Insurance £20.80, the total annual cost is around £40 million. A Cochrane systematic review of 21 trials of wart treatments with placebo groups reported a mean clearance rate of 27 % (range 0–73 %) in the placebo groups after a mean 15 weeks (range 4–24) [5]. In clinical practice, salicylic acid (SA) and cryotherapy are the most common treatments (all other treatments are off-label in France). In the Cochrane review, SA significantly increased the possibility of clearance of warts from all sites (risk ratio [RR] 1.56, 95 % confidence interval [CI] 1.20 to 2.03). A meta-analysis of cryotherapy vs. placebo for warts at all sites favoured neither the treatment nor the control (RR 1.45, 95 % CI 0.65 to 3.23). Evidence was insufficient for all other treatments — topical 5-fluorouracil (5-FU), imiquimod, dynamic phototherapy or intralesional bleomycin — to support their use, although they are broadly used as second-line treatment.

Patients often still seek treatment where their warts are unsightly or painful, resulting in increasingly aggressive treatments [6,7]. Furthermore, many people treat warts themselves, using over-the-counter preparations [8]. In clinical practice, only warts unresponsive to SA are considered resistant and pose management problems.

The aim of this randomized controlled trial was to compare the success of 3 months’ treatment with 50 % SA, liquid nitrogen, 5 % 5-FU cream with tape, and 5 % imiquimod cream for plantar warts of any type (myrmecia or mosaic plantar warts) as second-line treatment following 5 weeks of daily application of 50 % SA and 1 week of wash-out.

# Patients and methods

## Trial design and population

This multicentre randomized trial (VeRrues plAntaIres en villE [VRAIE]; ClinicalTrials.gov NCT01059110) was conducted among French dermatologists in private practice and hospitals. Patients were recruited from 2 February 2010 to 29 October 2014. The trial was performed in accordance with the principles of the Declaration of Helsinki, and the protocol was approved by the local medical ethics committee (Comité de Protection des Personnes Île-De-France IV IRB00003835, September 8, 2008, EudraCT 2008–002790-12), Companies provided the trial drugs and preparations free of charge: 50 % SA ointment (Pommade Cochon®; Tradiphar, Lille, France); colourless lacquer (Balleul-Biorga, Geneva, Switzerland), occlusive dressing (Blenderm®; 3 M, Leiden, The Netherlands), imiquimod (Aldara®) and 5 % 5-FU cream (Efudix®) (Meda Pharma B.V., Solna, Sweden). No company had any role in the trial design, data collection or analysis, or the writing of the manuscript. The study was supported by grants from the French Dermatology Society and by Meda Pharma.

Patients aged ≥ 18 years with a clinical diagnosis of plantar warts (myrmecia or mosaic warts) were eligible. Myrmecia warts are distinguished by the presence of a sharply delineated, rounded lesion with a rough keratotic surface that is surrounded by a smooth collar of thickened horn [9]. On dermatoscopy, such warts are characterized by multiple, densely packed papillae, each containing a central red dot surrounded by a whitish halo. Irregularly distributed black dots, corresponding to thrombosed vessels, are also visible [10]. Patients were required to have no more than 10 myrmecia on both feet or the entire surface. Coalescence of warts into large plaques was defined as “mosaic”. Patients were included if the surface area of the mosaic warts was <10 cm2. The surface area was calculated using a ruler and translation layer. The wart was diagnosed by the patient’s own physician. Patients were not eligible if they had received any treatment for plantar warts (including cryotherapy) within 1 month prior to eligibility screening. Patients with a history of immunosuppression or who were receiving systemic immunosuppressive drugs were excluded. All patients provided written informed consent before randomization. Patients were recruited at dermatology practices (n = 42) (in France, dermatologists mainly work alone in private practices) or in hospital settings (n = 6).

During the eligibility period, patients were asked to apply 50 % SA ointment (Pommade Cochon®, Tradiphar, Lille, France) directly on the wart(s) once daily for 5 weeks. Peri-lesional skin was protected using a colourless lacquer (Verlim®, Balleul-Biorga, Geneva, Switzerland) and covered with an occlusive dressing (Blenderm®, 3 M, Leiden, the Netherlands) for 12 h. Once the dressing was removed, the warts were gently abraded with a disposable nail file [11]. After a week-long wash-out period, patients were randomized to one of the treatments (Fig. 1
                        ).

## Randomisation, treatment, and assessments

Patients were randomly assigned to one of four investigated treatments in a 1:1:1:1 ratio. Initially, a fifth arm using duct tape therapy was considered (occlusive dressing only). During the trial, the scientific literature showed that duct tape therapy was not superior to placebo [12], and this arm was thus eliminated 24 months after the beginning of inclusions. Randomization lists were computer-generated (Cleanweb® Telemedicine Technologies S.A.S, Boulogne-Billancourt, France). Owing to the nature of the trial medication, patients were aware of the treatment assignments.

The 50 % SA ointment (Pommade Cochon®, Tradiphar, Lille, France) was applied directly to the wart(s) once daily. Peri-lesional skin was protected with a colourless lacquer (Verlim®, Balleul-Biorga, Geneva, Switzerland) and covered with an occlusive dressing (Blenderm®, 3 M, Leiden, the Netherlands) for 12 h. Once the dressing was removed, the warts were gently abraded with a disposable nail file.

The 5 % imiquimod cream (Aldara®, Meda Pharma B.V., Solna, Sweden) was self-applied once daily, 3 days a week (Monday, Wednesday, Friday) for 90 days without occlusive tape.

Fluorouracil 5-FU 5 % cream (Efudix®, Meda Pharma B.V., Solna, Sweden) was self-applied once daily and covered with a dressing (Blenderm®, 3 M, Leiden, the Netherlands) for 12 h for 90 days.

Liquid nitrogen was applied using a Cry-Ac® twice during each session (two freeze-and-thaw cycles), once a month for 90 days. A freezing halo of 2 mm was applied for at least 5 s.

For all patients, curettage of all warts was performed manually and patients were prescribed a 5-week course of 50 % SA followed by a 1-week wash-out period before inclusion and randomization. Thus, the included patients had warts that required second-line treatment. The initial treatment response was evaluated at 30 days post randomization.

## Outcomes

The primary outcome was complete remission for all warts, identified as the disappearance of keratin spots and keratotic plaques at 90 days. Standard photographs before and after treatment were evaluated by an independent committee unaware of the treatment used. Treatment failure was defined as a reduction of <50 % in the number or size of plantar warts at baseline and at 3 months. Secondary outcomes were the number of warts in remission as compared with baseline, the stability of remission, the relapse rate at 360 days and 720 days self-identified by the patient via a phone call, and the tolerability of the treatments on a visual analogue scale (0–10) at each visit (Fig. 1).

## HPV genotypes

Swabs from plantar warts were obtained from 97 patients before treatment and from 38 patients at 1–6 months after treatment. Swabs were collected by firmly rubbing a brush over the surface of the wart five times. Each brush was placed in a Cervical Specimen Transport Medium (Digene; Qiagen, France). DNA was extracted using a QIAamp DNA Mini Kit (Qiagen Courtaboeuf, France) in accordance with the manufacturer's instructions. Purified DNA was analysed for 46 beta-HPV types (HPV5, 8, 9, 12, 14, 15, 17, 19, 20, 21, 22, 23, 24, 25, 36, 37, 38, 47, 49, 75, 76, 80, 92, 93, 96, 98, 99, 100, 104, 105, 107, 110, 111, 113, 115, 118, 120, 122, 124, 143, 145, 150, 151, 152, 159, 174) and for 7 cutaneous-wart HPV types (1, 2, 3, 4, 10, 27, 57) by means of multiplex polymerase chain reaction (PCR) using the Multiplex PCR Kit (Qiagen). Typing of the specific HPVs involved hybridization of the PCR products to type-specific Luminex bead-coupled HPV probes as described [13].

## Sample size

Based on a complete remission rate of around 60 % for all warts using conventional treatment with a keratolytic acid agent (SA), it was determined that 109 patients/group for a statistical power level of 80 % were required to detect a difference of 20 % in remission rates between the standard treatment and other treatments using a chi-squared test. We considered adjustment of a two-sided alpha risk for multiplicity adapted to comparison with a control of several different groups [14]. Moreover, given the response rate of 33 % observed in the pre-inclusion period, we elected to enrol 660 patients.

## Statistical analysis

The database was extracted from the Cleanweb (Telemedecine) eCRF and transmitted to the investigator statistician, who performed the analyses independently. The main efficacy analysis concerned the modified intention-to-treat population, defined as all randomized patients who had taken at least one dose of the study treatment. The last-observation-carried-forward method was employed to address the missing number of lesions at Day 90. A complementary sensitivity analysis was conducted using the Markov Chain Monte Carlo (MCMC) multiple imputation method to ascertain whether differences between groups were dependent on the method for missing data imputation. Global comparisons between groups were made using the chi-squared test or Fisher’s exact test for binary variables, and the Kruskall-Wallis test for quantitative variables with non–Gaussian distribution. In the event of significance, groups were compared to conventional treatment with the keratolytic acid agent by means of a chi-squared test or Fisher’s exact test for binary variables, and the Mann-Whitney test for quantitative variables. All analyses were conducted using SAS 9.4 (SAS Institute Inc., Cary, NC).

# Results

We enrolled 358 patients (54 % of the target sample size) in the pre-inclusion period; 140 achieved complete remission during this period while 174 were ultimately included and randomized (Fig. 2
                     ). The median age was 38.4 years (range 27–46) and most patients were female (69 %) (Table 1
                     ). Myrmecia warts were the most predominant type of plantar warts (83.9 %) vs. mosaic warts (13.2 %) or both (2.8 %). For 149 patients (85.6 %), this was the first occurrence of warts at this particular site. The time to diagnosis was 14.8 ± 26.6 months. Overall, 25 (14.4 %) patients had a wart carrier in the household, 44 (25.3 %) walked barefoot at the gym and 80 (46 %) walked barefoot at the pool (Table 2
                     ). At inclusion, 41 patients were assigned to SA, 36 to cryotherapy, 33 to 5-FU, 42 to imiquimod and 22 to the duct-tape arm before it was eliminated (Fig. 2).

At Day 90, 6 (20 %) patients were in complete remission in the SA group, 3 (11 %) in the cryotherapy group, 1 (3.5 %) in the 5-FU group, 2 (6.6 %) in the imiquimod group, and none in the duct-tape therapy group. Each group had a notable number of patients lost to follow-up: 12 (28.5 %) in the SA group, 9 (25 %) in the cryotherapy group, 5 (15.1 %) in the 5-FU group, 12 (28.6 %) in the imiquimod group, and 5 (22.7 %) in the duct tape therapy group (Table 3
                     ). Note that a complementary sensitivity analysis using multiple imputation technics found very close estimations for differences between groups (SA vs cryotherapy 8.7 %, SA vs 5-FU 15.4 %, SA vs imiquimod 11.9 %).

Before treatment, cutaneous-associated HPV and beta HPV DNA were detected in 100 % and 57 % of swabs collected, for a mean number of 3.7 types of HPV. Among cutaneous-associated HPV types, HPV27 and HPV1 were predominant (90 % and 84 %, respectively). Despite a decrease in HPV1 prevalence (56 %) and the disappearance of HPV3, HPV4 and HPV10 types, the distribution of HPV types remained similar during follow-up (Fig. S1, supplementary material available online), irrespective of the treatment.

Two patients withdrew from the trial because of adverse events: 1 for a related adverse event in the SA group (painful fissure of the sole) and 1 for a non-related adverse event in the 5-FU group (kidney cancer). Overall, 10.1 % of patients experienced pain during the trial. Liquid nitrogen was the most painful treatment (n = 9, 25 %). Patients who received 5-FU experienced walking impairment more frequently than other groups (n = 3, 9.1 %). Of note, 2 patients in the SA group had had fractured metatarsals (Table S1, supplementary material available online).

# Discussion

VRAIE is the first major multi-arm study evaluating standard treatments for difficult-to-treat plantar warts, an issue for both patients and dermatologists. Difficult-to-treat or recalcitrant cutaneous warts have been addressed in previous studies [15,16] and a review [17], but no proper definitions have been proposed and no controlled study of this condition has been conducted. In VRAIE, to properly select difficult-to-treat cases of plantar warts, patients were allocated 5 weeks of 50 % SA after curettage — the first-line treatment for warts in a dermatology clinic—before initiation of treatment. Furthermore, we considered that this first phase of the study would reduce the risk of a placebo effect in the different groups. Indeed, the efficacy of SA during our pre-inclusion phase (39 %) was consistent with the published data for SA as first-line treatment for plantar warts [5].

The target sample size was not reached — 174 (40 %) of the 436 planned — so no statistical analysis could be performed to determine any differences between the arms. The lack of recruitment may have been due to the time-consuming procedure for dermatologists in private practice. In fact, difficult private-practice–based recruitment for randomised controlled trials has been reported in previous dermatology studies [18]. Better organization and facilities are mandatory for improving the external validity of randomised controlled trials of common skin diseases, allowing for better care of patients. However, the study provided some important information about the treatment of cutaneous warts. First and most importantly, no treatment had a substantial effect on difficult-to-treat warts, with at best, 20 % success in the SA group at day 90. This success rate for SA in patients who already received 5 weeks of SA should encourage treatment with SA for almost 3 months before treatment may be said to have failed.

Furthermore, the ancillary BIOVRAIE study showed the variety of HPV genotypes involved in plantar warts for the same lesion, with a mean of 3.7 genotypes found. Our data confirmed the high prevalence of alpha-genus HPV27 type and mu-genus HPV1 type in plantar warts, as previously demonstrated [19]. Furthermore, treatment response was not related to the persistence of these HPV types. The persistence of specific HPV types 1, 2, 4, 27 and 57 after treatment suggest that they could influence treatment outcomes.

As stated by the 2012 Cochrane review, the methodological quality of evidence concerning warts is poor, and with the methodological heterogeneity of many trials, pooling of data in a meta-analysis is problematic [5]. New treatments for cutaneous warts are being evaluated and include topical ionic contra-viral therapy with digoxin and furosemide [20]. Another promising therapy is an HPV vaccine. Reports of non-designed studies to treat cutaneous HPV but to prevent mucosal HPV [21], and now randomized clinical trials and a review, have shown some efficacy but with low quality of evidence [15,22]. In France, a randomized multicentre trial is ongoing, comparing nonavalent HPV vaccine to placebo for difficult-to-treat palmoplantar warts (NCT04814446).

# Conclusion

VRAIE failed to include the number of patients needed for statistical analysis. Nonetheless, the study demonstrated that no second-line treatment showed promising results after at least 3 months of SA and thus should not be used in further trials. HPV genotypes were heterogenous in plantar warts, possibly affecting treatment response. New treatments showing clear efficacy as compared with SA or new multi-group studies of resistance to first-line treatment plantar warts are needed.

# Ethics statement

The patients described in this manuscript provided written informed consent to publication of their case details.

# Funding sources

Société Française de Dermatologie (SFD) and Meda-Pharma provided financial support. Balleul-Biorga, Geneva, Switzerland; 3 M, Leiden, the Netherlands; Meda Pharma B.V., Solna, Sweden; and Tradiphar, Lille, France provided all treatments free of charge.

# Data availability

All data are available upon request.

The authors would like to thank the physicians and professors Feton-Danou, Levet, Legoux, Geoffray, Outtas, Gabillot, Vermeulen, Seiller, Ly, Gaboriaux, Andreani, Guillot, Francois, Colomb, Buzenet, Misery, Gand-Gavanou, Mussot, Vigan, Perrin-Nicolet, Ostojic, Morel-Nguyen, Vaillant, Guieu-Leman, Corgibet, Carbonnet and Balloy for recruiting patients, as well as all patients included in the VRAIE study.