"İdim" is "I was". Nowadays, it's usually written together with the previous word (e.g. hasta idim = hastaydım = I was ill; kütüphanede idim = kütüphanedeydim = I was at the library; müdür idim = müdürdüm = I was a director).
So the literal translation of this is "I was skin cancer". So extrapolating that to other tenses, if I wanted to say "I have skin cancer", would you say "cilt kanseriyim"?