Lots of things, from an alcoholic drink the weekend before to an aspirin (for the hangover?) can cause liver enzymes to be elevated. I've had elevated liver enzymes before, and the first time...it scared the be-jesus out of me. Sounds like your onc is on the ball and keeping an eye out, just in case. So as MK would say, "try not to worry til you know you have something to worry about."
"There's a difference between a philosophy and a bumper sticker." --Charles Schulz