My son, now eight, has had an extremely hairy back basically all his
life.  More accurately, he has this patch, about four inches wide and
six inches high, a bit off-center in the middle of his lower back,
covered with thick, animal-like hair.  The hair falls over his
waistband of his underwear almost like a tail.  And one of his legs is
unusually hairy for a kid that age, much moreso than the other leg
(although nowhere nearly as hairy as the spot on his back).  All the
hair - back, leg, etc., is the same light brown, almost blond, color of
the hair on his head.

His pediatrician advised us to see a pediatric dermatologist to rule
out the chances of it being a "hairy nevus."  As I understand this, if
the area were a hairy nevus, it would be at high risk for melanoma when
he's an adult, and, for safety's sake, should be taken out using skin
grafts and/or cosmetic surgery.

My son's skin color is unchanged under this mass of hair - in other
words, his skin color is consistent across his back and across his
body.  All the hairy nevus pictures I've seen on the web look more like
huge moles, or massive skin discolorations.

Just based on the information above, what are the chances he has a
hairy nevus?  And what does this mean in terms of cancer or other
life-affecting diseases?