Is cancer the theme for the decorations?

You don't mention the venue at all.  Where is this happening, outdoors, in a hall, a school, theater, golf course, and so on?

Is it a formal event or casual one?  Will there be children in attendance?  Will there cancer survivors in attendance?  Will there be patients in attendance?  Is this an expensive affair, or a low budget project?

I need to know all of these things, and probably more, before I could start suggesting anything other than to surf the web for pictures of cancer benefits and see what other people did.

Here is an example of symbolism from the American Cancer Society, and below are pictures of assorted fundraisers.  I skipped the breast cancer cake, but you should look for it.