I masturbate by rubbing a spot on the underside of my penis about an inch below the glans (I am circumcised). Since I'm in my mid 40's, I've been masturbating this way for over 30 years. Within the last year, a brown freckle-like spot (irregularly-shaped) has appeared right on the area I rub. When I first noticed it, I assumed it was some sort of bruising resulting from the rubbing and that it would eventually disappear. But after 5 or 6 months it is still there and hasn't changed at all in appearance. It is not painful or lumpy, simply brown. I saw a dermatologist and she recommended a biopsy. I elected to postpone that at the time because I was afraid of having skin removed from the primary spot on my penis that is sexually responsive. I have two questions:

1) Is this common? Has anyone had a similar experience (brown freckle-like spots appearing on the penis)? If so, should I expect them to go away?
2) Is it safe to have a biopsy performed on this area; ie, will the skin grow back with the same sexual responsiveness?