Abstract
Large congenital melanocytic nevus has a high risk of malignancy. However, few studies have summarized its characteristics, treatments, outcomes and malignancy incidence in Chinese patients. This paper reviews a retrospective cohort study evaluating 1,171 patients from Shanghai Ninth People's Hospital between 1 January 1989 and 31 August 2019 using electronic medical records and phone calls to collect clinical and pathological data in which 133 patients were diagnosed with a large congenital melanocytic nevus. Three patients relapsed, and none developed melanoma among the qualified patients. Besides, a new “7B” rule for distribution patterns of large congenital melanocytic nevi was proposed, including bonce, bolero, back, bathing trunk, breast/belly, body extremity, and body. The most common distribution pattern of large congenital melanocytic nevi was bonce, and all blue nevi distributed as bonce. Statistical analysis showed a significant difference (P = 0.0249) in the “7B” patterns between the melanocytic nevus and the neuronevus. In conclusion, the malignancy rate of large congenital melanocytic nevi is much lower in China than in other regions and people of other races. The pathology of large congenital melanocytic nevus may decide its “7B” distribution pattern.
Highlights
Large congenital melanocytic nevus (LCMN) is a rare disease that occurs in a range of ∼1 in 20,000 to 1 in 500,000 newborns [1, 2]
One hundred thirty-three patients were diagnosed with LCMNs between 1/1/1989 and 8/31/2019 and included 58 (43.6%)
Myasthenia gravis was present as a neurological symptom in one (0.7%) patient
Summary
Large congenital melanocytic nevus (LCMN) is a rare disease that occurs in a range of ∼1 in 20,000 to 1 in 500,000 newborns [1, 2]. It is acknowledged that the most common somatic mutation in congenital melanocytic nevi (CMNs) is NRAS mutation, but there are potential alternative mechanisms. One recent research showed that NRAS mutation existed only in 57.1% of large/giant CMNs. The remains had gene fusions or point mutations involving other genes, such as BRAF [3]. Extensive research has demonstrated that LCMN conveys a high risk for melanoma formation. Price et al [6] demonstrated that ∼5% of LCMNs transforms into melanoma, and half of these transformations occur early in life
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