Uhm. D:
It's a really lame idea, but at least it's an idea. DX ;;
Use Crabby the Hermit in an avatar?
Since Cancer = the crab in the context of the zodiac.
/shot
Erm I have an idea, how about have a ribbon on your avatar?
Can be posh ribbon, mystic Ribbon, any items with ribbons like Magical Girl etc?
And the ribbon can be in the colour of a type of cancer you want to support, like pink for breast cancer?