How To Get Rid Of Itching Black Lesion On Leg?

I have a black lesion on my lower left leg and its the size of the head of a crayola crayon thats been used. It itches like crazy on occassion I only scratch around the lesion. However, the lesion at times comes to a sharp point and this has fallen off and then it is very itchy. I hate to say this but I've had this lesion for about 5 yrs now.