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Note what signs you see.
I (W. Wertelecki, M.D.) see a giant congenital melanocytic Nevus (GCMN), more often referred to (erroneously) as bathing trunk nevus. In essence this condition is a neuro-cutaneous melanocytosis or dysplasia. GCMN is a high cancer risk syndrome (over 1% of patients develop a melanoma).
PERSPECTIVE: please, see the rest of the images of this patient and related comments.