Sugar Sources

I've heard many places that sugar feeds cancer. My sister in law was diagnosed with breast cancer last week and her doctor told her the same thing. (I don't normally eat much processed sugar but I do eat natural sugars.) I changed my settings & I'm tracking my sugar now. I am surprised to see that I exceed sugar every single day! I usually double it - sometimes triple it. Looking back, most of the sugar that I consume comes from 1% milk and fruit... Does the same thing apply to cancer & natural sugars?