23.4.3.1 Skin Cancer
Unlike the well-established mechanism by which UV radiation can induce DNA mutations [137,138] leading to skin cancers [139], there is no scientific evidence that thermal energy from nonionizing IR-laser radiation can induce, promote, or progress cancer development [140]. It has been reported that IR exposure may provide some protective benefit against cytotoxicity of shorter wavelengths of UV [141], possibly through a p53 mechanism [142].
Wulf and colleagues have investigated the effects of laser treatment alone, and before and after UV exposure on tumor formation in a well-studied animal model, lightly pigmented hairless mice. In one such study, lightly pigmented hairless mice were exposed to different fluences from a copper laser (578 nm), followed by solar-simulated radiation 4 times per week for 18 months. One laser treatment did not have any effect on skin tumor formation, alone, or in combination with UV [143]. In a similarly designed study, lightly pigmented hairless mice were treated up to 6 times with a 1060 nm CO2 laser before or after solar – simulated UV exposure. The CO2 laser had no effect on skin tumor formation, and did not have an effect on UV-induced skin tumor formation [144]. Finally, the effects of nonablative IPL, alone and in combination with solar-simulated UV, were studied [145]. The IPL had no effect on skin tumor formation in the lightly pigmented hairless mice, nor did it affect UV – induced tumor formation. These data are supportive of the view that laser treatment alone has no effect on the development of skin tumors nor does it have an impact on solar-simulated skin tumor formation in a well-established animal model.
The studies in animals corroborate clinical findings which, to date, have found that lasers used in cosmetic dermatology for the past two decades have no effect on the incidence of skin cancer. Nevertheless, some concerns remain, particularly as it relates to the treatment of pigmented skin lesions such as dysplastic and pre-melanocytic nevi with lasers [146]. In the course of laser treatment for hair removal or skin rejuvenation, it is likely that dysplastic nevi get inadvertently exposed on a regular basis. Again, to date, there have been no reported cases of melanoma or nonmelanoma skin cancers as a result of laser treatments.
The standard treatment modality for congenital melanocytic nevi used to be surgical excision. However, lasers treatments are now being increasingly used on these nevi to provide better cosmetic and therapeutic benefits [13,147-150]. There have been no reported cases of skin cancer from these treatments. Theoretically, reducing the number of melanocytes in these lesions reduces the number of cells that have a malignant potential. An 8-year follow up study of 85 patients with congenital nevi treated with the ruby laser showed no evidence of melanoma formation [151]. Histological analysis of the treated skin biopsy samples performed on select patients in this study also showed no evidence of melanoma, squamous cell carcinoma, or sarcoma formation. In a recent study, Goldberg et al. looked at four different markers for malignant transformation after exposing benign nevi to Q-switched Nd:YAG laser [152]. No significant increase or presence of the malignant transformation markers was seen in the exposed samples. In conclusion, the scientific evidence suggests that the risk for inducing cancer with laser treatment in either healthy skin or skin with lesions is extremely low, if not negligible.