atheism, philosophy and emotional immaturity

[Joel]

Prove that it is a fallacy to say "My doctor told me cigarettes cause cancer so based only on this, it is likely that cigarettes cause cancer". Where does fallacious reasoning enter that?

That's not the same as "My doctor said cigarettes cause cancer, therefore cigarettes cause cancer."

What you said is not fallacious. It is trust. "I trust that he is correct, because he is more knowledgeable than I on this subject."

EDIT: Though, reading your quote, I may disagree... With myself.
"based on only this" do you mean therefore?