As a cancer survivor myself maybe I can give some insight. When you are sick you find out who your friends are. Two of my good friends came to visit me in the hospital and at home. I truly appreciated the fact that they took time out of their day to see how I was doing. It didn't matter what they said, it was enough that they cared enough to make an appearance.
Compare that to the people that "I didn't want to bother you in this difficult time". This is more about them being afraid of saying something wrong and not being able to do anything for you. A simple statement like "Man, I'm so sorry you and your family are going thru this" is enough.