Laser Treatment of Nevomelanocytic Nevi: Can Results From an Asian Study Be Applicable to the White Population?

I read with interest the Editorial Review regarding the use of laser in the treatment of pigmented lesions.¹ I share the authors' concern that there is a lack of long-term studies regarding the use of laser in the treatment of nevomelanocytic nevi. Therefore, the issue is whether one should use laser to treat these lesions at all or be selective, as suggested by the authors of the article.

Like many of my colleagues in Asia, I frequently use laser to treat facial melanocytic nevus. Indeed, the only long-term follow-up study is from Japan when Imayama and Ueda² reported no histological evidence of malignant changes 8 years after normal ruby laser treatment for congenital nevi. This is not due to a difference in therapeutic approach, and I do not believe we are necessarily more aggressive than our Western colleagues. A more important reason is the differences in the biological behavior of melanocytes among patients from different ethnic origins. As pointed out by Stratigos et al,¹ the potential deleterious effect of laser exposure is malignant transformation. Unlike in the white population, melanoma is uncommon among Asians and differences in skin type are unlikely to be the main reason. Data from the Osaka Cancer Registry (1964-1995) indicated that the average annual age-standardized incidence rates per 1 million population were 2.45 for men and 2.04 for women.³ This compares with the Italian data (also dark skin type), which indicated much higher figures, with average annual age-standardized incidence rates (1992-1997) per 1 million population of 100.4 for men and 130.9 for women (ie, 10.04/100 000 for men and 13.09/100 000 for women).⁴ Furthermore, most of the melanoma encountered among the Asian population tends to be acral in nature. The reason for such differences is likely to be related to genetic variation. I am not aware of any study that looked at the p16ink4a gene expression among Asians. All these factors indicate that results from Asian studies cannot be applied to whites.

Stratigos et al also suggested that unlike UV radiation, the effects of lasers on tissue are primarily thermal. In this aspect, I would like to point out the preliminary in vitro study data that indicate that after sublethal laser damage on melanoma cell line, there is an alternation in the integrin expression pattern.^{5 - 6} Such changes can lead to a rise in melanoma cells' motility, which in turn suggests an increase in the metastatic potential. Although the biological behavior of melanoma cell lines may not truly reflect that of nevoid melanocytes, these changes at least indicate that the sublethal effect of laser is more than thermal in nature.

Taking the above factors into consideration, I believe the use of laser for the removal of nevomelanocytic nevus in whites should be considered as a form of experimental therapy. Even for Asians, such use should be avoided if the lesion is located in acral areas or if there is any other risk of melanoma, including previous history or family history of melanoma, and clinical evidence of atypia.