Letter in response to the article: “A retrospective case series of ten patients with malignant melanomas arising from small- and medium-sized congenital melanocytic nevi in South Koreans”

Sir,

We read with great interest the paper recently published in your esteemed Journal by Kim et al.¹ In their retrospective analysis, the authors showed a melanoma incidence rate of 2.7% in a group of 377 small (<1.5 cm) and medium (1.5–19.9 cm) congenital melanocytic nevi followed over a period of 6.5 years. This study emphasizes a possible underestimation of the risk of malignant transformation of such lesions, especially those of medium size, which showed a higher incidence rate compared to small congenital melanocytic nevi (2.7% vs. 2.2%). Indeed, based on available literature data, the risk of malignant transformation of small/ medium congenital melanocytic nevi would be quite lower with an overall incidence of melanoma associated with this type of nevi being less than one percent (0–1.3%).²

Of note, the reasons underlying the discrepancy between the study by Kim et al. and previous data have not been addressed by the authors. In our opinion, one of the explanations could be the lack of prospective/retrospective analyses on small/ medium congenital melanocytic nevi following patients in adulthood as most of the published longitudinal studies focused on young subjects with no adult age monitoring. This is a significant bias since small/medium congenital melanocytic nevi-associated melanoma tends to spare prepubertal children and occur during adulthood. This is consistent with data observed in the analysis by Kim et al., in which the mean age of patients with malignant transformation was 49.2 years. In addition, the likelihood of developing melanoma in small/ medium congenital melanocytic nevi has been often evaluated without stratifying the risk between these nevi or according to the size in the previous studies. This is another potential bias as it is possible that the risk of melanoma in such nevi might vary between small and medium lesions but also based on the size in the context of medium congenital melanocytic nevi with larger lesions having a greater incidence.

In our opinion, the study by Kim et al. and the above-mentioned biases concerning existing literature data should stimulate researchers to set prospective analyses on patients with small/medium congenital melanocytic nevi including adult age monitoring as it is possible there is an underestimation of melanoma risk in such lesions, especially those of greater size. Only a better knowledge on the lifetime risk of malignant transformation may ensure a correct management of these nevi.

In this regard, two main strategies have been suggested for non-suspicious lesions, that is, periodic clinical and/ or dermoscopic monitoring and prophylactic excision.³ Regarding the latter option, the ideal timing would be before the age of 11 since this has been reported as the minimum age of small/medium congenital melanocytic nevi-associated melanoma development by several studies. However, some surgical factors need to be taken into account about the optimal timing of excision to achieve the best possible esthetic outcome, mainly including lesions size and location. While the impact of the former factor is intuitive, we would like to make a specific consideration on the latter variable. The projected adult size is different in relation to the considered anatomical region. As suggested by Krengel et al.,⁴ from birth to adulthood, the area of the head grows by a factor of 2.8, trunk and upper limbs by a factor of eight and lower limbs by a factor of 12. Therefore, the surgical excision should always be performed considering the growth potential of the region.

The lesions located on/near joints or genital area are the most challenging ones as their excision might result in scar contractures with consequent possible functional problems, pain and esthetics issues.

In our experience, the direct closure must always be performed whenever possible. In addition, the incision should be made perpendicular to the direction of growth so as to change as little as possible over the years. The skin graft should be made at full thickness so as to retract as little as possible.

Finally, the flaps should be harvested considering the growth lines and the anatomical region of the donor site.

The growth phase of the patient which begins and ends earlier in women (12–16 years) than in men (14–18 years) could be defined “dynamic phases” in the surgical treatment. This phase is typified by a very accelerated growth and, therefore, it is not advisable to defer surgery.