CONGENITAL MELANOCYTIC NEVI WITH PLACENTAL INFILTRATION BY MELANOCYTES - A BENIGN CONDITION THAT MIMICS METASTATIC MELANOMA

Background: Placental metastases from cutaneous malignant melanoma hor n both the mother and the fetus have been reported. The finding of ben ign-appearing melanocytes in the placenta in association with congenit al melanocytic nevi (CMN) is more exceptional, with only 6 reports in the literature. Clinically, the finding of melanocytes in the placenta in this setting can be alarming and might erroneously lead to the dia gnosis of metastatic melanoma. Observations: Herein, we describe 3 add itional patients with CMN with placental infiltration by melanocytes w ith a benign phenotype. In the results of immunoperoxidase stains, the melanocytic cells were positive for S-100 protein and HMB-45 in the 2 lesions available for study. Staining of placental vessels with Ulex europaeus agglutinin I (Vector Laboratories, Burlingame, Calif) failed to show intravascular melanocytes in the 1 lesion available for study . We report for the first time DNA diploidy in 2 lesions available for study, which were analyzed by DNA image cytometry. We describe the fi rst patient with a relatively small, nongiant CMN. Conclusions: We sup port the notion of the aberrant migration of melanocytes from the neur al crest during fetal development as the most likely explanation of th is phenomenon and note the similarity to the association of CMN and le ptomeningeal melanocytosis. However, the precise histogenesis of this process remains uncertain. Most importantly, our data provide further evidence for the benign nature of this condition. Awareness of this en tity is of vital importance in avoiding overdiagnosis of melanoma in t his clinical setting.