**3.3 Debulking**

Debulking (or deep curettage) is considered a surgical procedure and it is often used in thicker lesions, reducing as much as possible the total volume. This procedure is usually performed either immediately or a few weeks before PDT [15, 23].

Even though it is considered a more invasive procedure compared with the simple curettage, it can be applied without anesthesia. The cosmetic outcome is considered favorable [23] and allows a significant reduction of the BCC thickness, which makes nodular lesions more responsive to the treatment [24, 25].

Whereas the topical PDT efficiency is about 72% when a previous debulking lesion is not applied, for debulked lesions this efficiency can increase up to 92% [23, 26]. Therefore, the debulking associated with PDT is a relevant option for multiple, pigmented, and nodular lesions, improving clinical response [27].

#### **3.4 Ablative fractional laser**

This technique consists of using a laser source to create ablated channels on the lesion surface, vaporizing a small portion of the tissue [28]. Usually, lasers with excitation wavelengths in far-infrared spectrum are used, due to the high absorption by the water in the tissue [29, 30]. The main types used are CO2-laser (10,600 nm), Er:YAG-laser (Erbium yttrium aluminum garnet, 2940 nm), and Er:YSSG-laser (Yttrium scandium gallium garnet, 2790 nm) [13].

The depth of the microchannels created varies according to the laser energy. The energies between 32 mJ and 380 mJ generate microchannels with a depth between 300 μm and 2100 μm [31]. Due to the increased skin penetration, this procedure makes PpIX fluorescence both more intense and homogeneous in deeper skin regions, and this can be controlled by adequately adjusting laser energy density [32, 33].

Studies using CO2 laser associated with PDT for lesions treatments showed an increase of about 20% in the clearance of different protocols comparing the treatment without and with the use of laser, respectively [34–36]. Although it is a reliable and effective method, it is also a more invasive procedure with a high potential for skin damage with scarring, discoloration, and even infection. Besides that, the costs of the devices are considered high compared with the abovementioned techniques [37].

#### **3.5 Microneedles**

Needles and especially microneedles (MNs) have been used as a method to enhance drug permeation through SC [38]. MNs have the advantages of being minimally invasive, its application is simple, well accepted by the patients, and it is cost-effective [39]. MNs have been developed with lengths up to 900 μm to avoid penetrating in vascular and nervous regions. Therefore, MNs can penetrate the SC without stimulating pain receptors, which is another advantage [40].

The MNs size cannot be seen by patients, thus reducing possible needle phobia. MNs have strong mechanical properties to enable disruption and penetration through the SC, reaching successfully the deeper skin layers without causing any bleeding due to the small length of needles [13].

There are MNs with different shapes (tetrahedron, pyramidal, conical, beveled tip, or tapered cone) that promote different insertion pathways and permeation into the skin. They also can be divided according to the material, such as solid (metallic) or polymeric (hydrogel or dissolving) types, and can be assembled either as a roller or as low-cost patches. The MNs can also be produced with a drug coating on their surface, to facilitate delivery, or hollow, to promote the delivery through channels [13]. The use of MNs rollers for enhancing penetration of topical cosmeceuticals has been well described and transdermal patches can be used easily by anyone [13, 39].

Some studies described a higher formation of PpIX in deeper skin regions when MNs are used and compared with topical application in animal models [41, 42]. A

recent paper by Requena *et al.* explored dissolving MNs containing ALA. The PpIX fluorescence intensity showed to be 5-times higher at 0.5 mm on average compared with cream in *in vivo* tumor mice model [43].

Solid MNs have been commonly used for skin pretreatment before conventional PDT, promoting a good PDT response for actinic keratosis [39]. However, their use for the treatment of BCC or squamous cell carcinoma SCC has not been investigated yet [13].
