Malignant melanoma in children and congenital melanocytic nevi: DNA content and cell cycle analysis by flow cytometry.

Malignant melanoma (MM) in children, although a rare neoplasm, can occur within a preexisting congenital melanocytic nevus (CMN). All the potential risk factors for this phenomenon are not well known, but increases in S phase and G2 + M phase of cell cycle, DNA aneuploidy, and cell cycle abnormalities in precursor lesions might be among the risk factors. Using paraffin-embedded tissue, we performed a retrospective analysis of DNA content, aneuploidy, and cell cycle by flow cytometry. Two groups of patients were analyzed: 28 children with CMN who did not developed MM, and 6 patients who further developed MM. In this second group, three patients had four biopsies done before the appearance of MM and in two patients biopsies were done after the appearance of MM. All CMN not associated with MM exhibited diploid cells only, their S phase was 11.5% (+/- 3.8), and their G2 + M phase was 2.5% (+/- 2.2). Among those patients who developed MM, 3/6 had an S phase > 15.5 and a G2 + M phase > 2.3 prior to the appearance of MM. Two out of six patients had a tetraploid DNA when MM developed and died with a disseminated MM. They had an S phase > 15.5 and their G2 + M phase was > 2.5. We propose that evaluation of DNA content and cell cycle by flow cytometry is a useful method to supplement biopsy findings in children with CMN who have lesions suspicious of developing a MM.