HP40 was recently FDA-approved to treat raised SKs and as demonstrated by the two cases presented here, this in-office treatment can lead to positive therapeutic outcomes for SKs located in cosmetically-sensitive areas. The mechanism by which HP40 destroys SKs is not fully understood, but it likely utilizes the oxidizing potential of H2O2.28 H2O2 can directly damage cell components as a reactive oxygen species and form hydroxyl free radicals to exert further oxidative damage.29 Applied at supraphysiologic doses, HP40 delivers a fraction of the dose through the stratum corneum (SC) to the epidermis, where it can generate free radicals by overcoming the skin’s antioxidant capabilities and initiate cellular apoptosis and necrosis. Because of this mechanism, HP40 should not be applied to open or infected SKs where the SC is compromised. The SC protects deep tissue from high concentration H2O2 so without this barrier, H2O2 can cause rapid death of nearby cells.30 However, when used properly in phase 3 trials, side effects of HP40 were limited to local skin reactions, the majority being mild to moderate.26 Scarring, hypopigmentation, and hyperpigmentation occurred in less than 1%, 3.0%, and 7.8% of sites treated with HP40, respectively.26 Although, nearly all of the participants were Fitzpatrick Skin Types I to IV, so the effect of HP40 on darker skin is less clear.26 In an ex vivo model of human Fitzpatrick Skin Type V, HP40 was less toxic to melanocytes compared to cryotherapy.31 Therefore, HP40 may be superior to cryotherapy for skin of color, but large, controlled studies including multiple skin types are needed to compare these therapies.
In support of HP40’s potential to minimize the risk of scarring and pigmentary changes, the patient in Case 1 was previously treated with cryotherapy, which led to hypopigmented scarring. However, as seen in Figure 1D, there was no evidence of scarring or hypopigmentation from HP40 after over three months. The patient in Case 2 with Fitzpatrick Skin Type IV was similarly spared of these adverse effects. While HP40 still has a small risk of scarring and pigmentary changes, this is a good option to discuss with patients who want to minimize the side effects from treating SKs in visible skin areas.
Selecting a therapeutic strategy for SK removal requires consideration of the location of SKs as well as the patient’s skin type and expectations of what will be left behind after removal. Given HP40 is not covered by insurance and multiple treatments may be needed, patients with SKs in non-cosmetically sensitive areas may prefer treatment with cryotherapy, curettage, or electrodessication. However, patients with SKs in cosmeticallysensitive areas like the face and neck, particularly those with dark skin types, may benefit from a topical therapy like HP40 that is less cytotoxic to melanocytes and the neighboring epidermis. 31 This is especially true if patients are dissatisfied with previous treatments. Further, as demonstrated by phase 3 trials26 and based on the author’s experience, raised SKs on the face and neck respond especially well to treatment with HP40.
In addition to instructions provided by the manufacturer, the following practical considerations based on the author’s experience may be helpful when using HP40. It is important to apply firm pressure and cover the entire lesion, while staying within a 2 to 3 millimeter margin of the SK to avoid contact with normal skin. Four treatment cycles are recommended for each SK, but if the patient experiences 6 to 7 or more pain on a scale of 0 to 10, the treatment should be terminated. Additionally, when treating SKs near the orbital rim, some eyelid swelling is expected; reassure the patient that this usually resolves in a few hours.
Overall, HP40 is a new therapeutic option for SKs that can be discussed with patients. As demonstrated by the cases presented here, HP40 is particularly useful for SKs on the face and neck and may avoid the scarring and hypopigmentation that can occur with cryotherapy. Future examination of HP40 in patients with dark skin types is needed to confirm our suspicion that HP40 may lead to less pigmentary changes than non-topical, invasive therapies.
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