You might be amazed to know how few individuals are directly benefitted and helped when they are dealing with cancer. It really may not be anywhere near as good as it sounds. If you really want your donation to count, consider staying away from those who do not directly impact those affected.
Man, I hate saying this stuff. But what I hate more is knowing how deeply, and crucially, affected people are by a diagnosis and have no help, while organizations that play on people's desire to help walk around with millions.
If you know anyone with cancer, and they are willing to talk about it, ask them if they have ever benefitted from an organization in a way that really matters and counts in a way that is tangible, practical, and really makes a difference. If the answer is yes, great, find out more. It is rare.
I think most people don't have a clue until they have a need, and then they find out there is very little that can actually help. It is kinda being dropped in the middle of an ocean thinking there is help around when you need it. But then when you start to yell for help, all of those who seemed to be able to help either are not within earshot or tell you, "sorry...our resources are not for people like you. Yes, we help in some cases, you just do not fit our parameters. You are going to drown? See if someone else can help."
Give wherever you like. As if you needed my permission. :p All I ask is that you become more aware of why you give your money to the organizations you do - especially if it is in your heart to truly make a difference.