I had a SCCIS removed from my thigh in Jan 2017 and recently had a recurrence just outside the scarred area. My derm said that it's a new tumor, not a recurrence, and told me that that an area of skin that was sufficiently sun-damaged has an inherently higher risk for tumor formation, which she called the "field effect." So keep a watchful eye out!
I'm trying 5FU first, but I suspect surgery is in my future