Yes, I have smelled it too. Not only cancers. I can smell other diseases too. When somebody has a couple of days left to live, they have a perticular smell. I used to work at a hospital, so I have noticed cancer and before-death-smell a lot.
My family used to use my "dog-nose" to smell if food where rancid or moldy, I could always smell it long before anyone else could. I can sometimes smell where women are in their menstrual cycle. For what I need that talent, I do not know. It is sometimes a blessing, and sometimes a curse.