There are lots of different characteristics between normally functioning cells and cancerous ones. Cancer cells are a clump of many harmful cells that multiply and divide, whereas healthy cells don't clump as largely. They also differ in shape and size. Cancer cells have a larger and darker nucleus and they also have an abnormal amount of chromosomes.
Hope this helps :)
If you need any more info let me know and I can give you more differences. These are just the basic differences.