Combination of Congenital and Deep Penetrating Nevus by Acquisition of β-Catenin Activation.

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Deep penetrating nevus (DPN) is an intradermal, sometimes compound benign melanocytic lesion, which involves the reticular dermis, occasionally reaching the subcutis, which can raise concern for melanoma both clinically and histologically. Recently, it has been genetically defined by the combination of MAPK activating and β-catenin activating mutations. We sought to investigate genetic alterations in 2 cases of combined nevi of congenital melanocytic and DPN. Case 1 was a 16-year-old woman with a pigmented lesion on the trunk since birth, which was completely excised. Histopathological examination revealed a combined congenital nevus with a DPN. Comparative genomic hybridization showed no major genetic alterations, except for gain of 6q11.1 and point mutation of B-RAF V600E. Case 2 was a 62-year-old woman with a congenital pigmented lesion on the back. The lesion was diagnosed as a combined nevus of congenital and DPN. Comparative genomic hybridization showed no genetic alterations, and the NRAS Q61K was detected in both components. DPN is in most cases part of a combined nevus. Our cases showed strong and uniform nuclear expression of β-catenin and cyclin D1 in the DPN component suggesting the evolution of the congenital nevus to the DPN clone by acquiring β-catenin activating mutation.