Does bad smelling flatulence mean cancer?

This is unlikely. Nothing is impossible, but the inability to digest fat can lead to this. The hardest part of your question is defining bad smelling flatulence: many feel it all smells bad. Sometimes getting ones gut flora back to a normal state can help: yogurt and probiotics. But if you are worried, see your doctor for physical. It is not impossible if one cannot digest fat due to cancer to have this sign.