Lesion dimensions following ablative fractional laser treatment in non-melanoma skin cancer and premalignant lesions

Abstract

Non-melanoma skin cancer (NMSC), which comprises basal cell carcinomas (BCC) and squamous cell carcinomas (SCC), is the most common human cancer with an estimated incidence of more than one million new cancers per year alone in the USA [1–5]. SCC may be preceded by precursor lesions such as actinic keratoses (AK) and SCC in situ (Bowen’s disease), whereas BCCs are regarded as invasive tumours from the beginning. The incidence of the premalignant lesions is even higher with a reported prevalence of AK at 15.4% in men over 40 years of age in a UK population [5]. Ablative fractional laser (AFXL) resurfacing has over the past 5 years gained increasing popularity due to its clinical efficacy and short healing times compared to conventional ablative laser treatment [6]. AFXL creates microscopic vertical channels in the skin, surrounded by undamaged viable tissue. These vertical laser channels, socalled microscopic ablation zones (MAZ), are surrounded by a microscopic treatment zone, which consists of a thin necrotic layer and a coagulated tissue zone [7]. Fractional ablative lasers are available as CO2 lasers (10,600 nm), erbium yttrium aluminium garnet lasers (Er:YAG, 2,940 nm) and yttrium scandium gallium garnet lasers (YSGG, 2,790 nm), all of which have a high absorption in the target chromophore, water, and thus target intraand extracellular water-rich components such as keratinocytes and vessels [6]. AFXL resurfacing is currently used in the treatment of photodamaged skin, wrinkles, and acne and burn scars, but so far not for malignant or premalignant lesions, which is the case for conventional ablative lasers [9–13]. The immediate tissue damage after AFXL and the dimensions of the laser-ablated channels can be characterized histologically [9, 15]. MAZ dimensions have previously been investigated in animal models [14] and normal skin [15–17], whereas no data to our knowledge are available on MAZ dimensions from NMSC and dysplastic lesions. As premalignant and malignant lesions differ histologically from normal skin in several aspects including content of cell types, tumour load, vascularization, and collagen and water content, AFXL may induce different ablation patterns in dysplastic skin and normal skin. Recently, AFXL-assisted drug delivery has been introduced as a novel treatment concept to intensify the biodistribution of topical pharmaceuticals [18]. In vivo studies in pigs have shown that AFXL enhances deep tissue penetration and photoactivation of topically applied methyl aminolevulinate, which is a photosensitizer used for photodynamic therapy (PDT) [18, 19]. PDT is based on photosensitizer uptake by tumour tissue followed by illumination with visible light, which in the presence of oxygen forms cytotoxic oxygen species, causing apoptosis and necrosis of tumour tissue. PDT is approved for the treatment of BCC and premalignant lesions with high cure rates of 90% being reported for superficial malignant lesions, but less effective cure rates of 70–80% for thicker lesions [20]. The inferior treatment outcome in thick lesions K. Togsverd-Bo (*) : C. S. Haak :M. Haedersdal Department of Dermatology, Bispebjerg Hospital, University of Copenhagen, Bispebjerg Bakke 23, 2400 Copenhagen, NV, Denmark e-mail: ktogsverdbo@dadlnet.dk