Provided herein are compositions, systems, kits, and methods for topically applying a composition to a
body area of interest adjacent to and having precancerous and / or cancerous cells (e.g.,
skin cancer cells), wherein the composition comprises N-phosphonacetyl-L-
aspartic acid (PALA) (also known as sparphosic acid) and water, and optionally further comprising at least one
nonionic surfactant.