Suggest Treatment For Lichenoid Keratosis

I have Lichenoid Keratosis on my lip. It has come back three times since Feb 2011. I have had it shot with Nitrogen. 1.5 weeks of healing time, then as soon as im back in the sun, it comes back... I use sun screen 45. The Plastic Surgeon said its in a bad spot to cut out.. Scaring and long heal time.. So, what do I do? Any help would be appreciated.... Is my outside life over?