Please help as I am extremely worried, I am a cancer survivor with new lump in arm skin. What are possibilities?

Your concern... ...Is entirely understandable, given your history. The chances that this new lump represents a recurrence of your cancer depends entirely on what kind of cancer you had, and other factors. Odds are that it is something entirely different, but go to your doctor right away and find out for sure. The sooner you find out it's just a cyst or lipoma, the sooner you can stop worrying.
Incomplete info. The lump needs to be examined and if warranted, excised and tissue examined by a pathologist. It is not practical to list possibilities without examining the patient and the lesion.
Needs evaluation. The lump needs to be seen by an md, and if suspicious, biopsied.