Risk of malignant transformation of congenital melanocytic nevi: a retrospective nationwide study from The Netherlands

Laura H Zaal, Wolter J Mooi, Helen Klip, Chantal M A M van der Horst
Plastic and Reconstructive Surgery 2005, 116 (7): 1902-9

PURPOSE: Since the risk of malignant transformation is the most important reason to remove congenital melanocytic nevi, and data vary in the literature, we aimed to determine the incidence of malignant transformation in congenital melanocytic nevi in The Netherlands.

METHODS: The Dutch nationwide pathology database, PALGA (Pathologisch Anatomisch Landelijk Geautomatiseerd Archief), provided anonymous pathology descriptions of all patients registered with congenital melanocytic nevi (giant or nongiant nevus) and of patients with a malignant melanoma within a congenital melanocytic nevus who were diagnosed between January 1, 1989, and December 31, 2000. A comparison was made between cancer incidence in our cohort of patients and the general population by applying the person-year distribution in the cohort to sex-, age- and calendar period-specific reference data obtained from The Netherlands Cancer Registry. Our cohort consisted of 3929 patients.

RESULTS: After a median follow-up time of 4.7 years, a total of 15 cases of malignant melanoma were observed in 19,253 person-years, against 1.23 expected cases. The incidence rate of malignant melanoma was greater than expected on the basis of population rates, overall standardized incidence rate of 12.2 (95 percent confidence interval 9.6 to 15.3). Compared with the general population rates, we observed an increased risk for malignant melanoma, both in men (standardized incidence ratio = 6.4; 95 percent confidence interval 4.1 to 9.6) and women (standardized incidence ratio = 14.1; 95 percent confidence interval 10.5 to 18.7). This is comparable with the higher propensity of women to develop a malignant melanoma. Patients with a giant nevus had a 51.6 percent higher risk of developing a malignant melanoma compared with the general population rates.

CONCLUSION: Our study shows that congenital melanocytic nevi have a significantly higher risk of developing a malignant melanoma compared with the age-, sex-, calendar-period-specific reference data from The Netherlands Cancer Registry.

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