Abstract: Background: Large congenital melanocytic nevus (LCMN) is considered a risk factor for melanoma, although the magnitude of this risk is controversial. Objective: To evaluate the risk of melanoma development in patients with LCMN seen at a dermatology referral center in Brazil during a twelve-year period. To the best of our knowledge, there are no published similar studies on large congenital melanocytic nevus in South America. Methods: Our prospective cohort included only patients with congenital nevi ≥20cm. The cumulative risk of developing melanoma and the standardized morbidity ratio were calculated for patients followed up prospectively for at least 1 month. Results: Sixty-three patients were enrolled in this study. One patient who developed melanoma prior to enrollment was excluded, and five were eliminated because of insufficient follow-up time. Mean follow-up for the remaining 57 patients was 5.5 years (median 5.2 years). Median age of entry into the study was 2.6 years. Most patients (75.4%) underwent only clinical observation. Melanomas occurred in 2 (3.5%) patients. Five-year cumulative risk for melanoma was 4.8% (95% CI: 1.9-11.5%). Standardized morbidity ratio was 1584 (95% CI: 266-5232, p<0.001). Study limitations: The small sample size reduces the accuracy of risk estimates. Conclusions: This study analyzed prospectively for the first time data from South America demonstrating that patients with LCMN have a higher risk of developing melanoma than the general population (p<0.001).

O nevo melanocítico congênito gigante é, geralmente, definido como lesão melanocítica presente ao nascimento e que atinge, no mínimo, 20 cm de diâmetro na vida adulta. Sua incidência é estimada em menos de 1:20.000 recém-nascidos. Contudo, apesar de sua raridade, possui importância tanto por estar associado a complicações graves, como o melanoma maligno e o acometimento do sistema nervoso central (melanose neurocutânea), quanto pelo grande impacto psicossocial que ocasiona no paciente e nos familiares, devido a seu aspecto comumente inestético. O nevo congênito gigante, geralmente, apresenta-se como lesão acastanhada, plana ou elevada, de bordas bem definidas e com hipertricose, e seu diagnóstico é eminentemente clínico. Do ponto de vista histológico, porém, os nevos melanocíticos congênitos são diferenciados dos nevos adquiridos, principalmente pelo seu tamanho maior, pela disseminação das células névicas para as camadas mais profundas da pele e pela sua arquitetura e morfologia mais variadas. O nevo congênito gigante é considerado fator de risco para o desenvolvimento do melanoma. Todavia, a real incidência de malignização ainda é controversa. Estima-se que o risco de melanoma ao longo da vida esteja entre 5 e 10%. Diante dessas incertezas e do tamanho das lesões, a abordagem do nevo gigante representa um desafio e deve ser individualizada. O tratamento pode incluir procedimentos cirúrgicos ou não cirúrgicos, intervenções psicológicas e/ou acompanhamento clínico, com atenção a mudanças de coloração, superfície ou textura do nevo. Considera-se que a única indicação absoluta para a intervenção cirúrgica é o surgimento de uma neoplasia maligna sobre a lesão.

Giant congenital melanocytic nevus is usually defined as a melanocytic lesion present at birth that will reach a diameter ≥ 20 cm in adulthood. Its incidence is estimated in <1:20,000 newborns. Despite its rarity, this lesion is important because it may associate with severe complications such as malignant melanoma, affect the central nervous system (neurocutaneous melanosis), and have major psychosocial impact on the patient and his family due to its unsightly appearance. Giant congenital melanocytic nevus generally presents as a brown lesion, with flat or mammilated surface, well-demarcated borders and hypertrichosis. Congenital melanocytic nevus is primarily a clinical diagnosis. However, congenital nevi are histologically distinguished from acquired nevi mainly by their larger size, the spread of the nevus cells to the deep layers of the skin and by their more varied architecture and morphology. Although giant congenital melanocytic nevus is recognized as a risk factor for the development of melanoma, the precise magnitude of this risk is still controversial. The estimated lifetime risk of developing melanoma varies from 5 to 10%. On account of these uncertainties and the size of the lesions, the management of giant congenital melanocytic nevus needs individualization. Treatment may include surgical and non-surgical procedures, psychological intervention and/or clinical follow-up, with special attention to changes in color, texture or on the surface of the lesion. The only absolute indication for surgery in giant congenital melanocytic nevus is the development of a malignant neoplasm on the lesion.