Do Normal Cells Also Inflame with Efudex

I am using Efudex for the first time, age 89. I understand its effect on, and reaction to, precancerous cells. If I apply it over a small area on my neck , about one inch square, will ALL the skin on the area react, crust, and erupt? OR: will only the precancerous cells do that?
Thank you all so much for this offered support.