How To Treat Fluid Around The Heart Despite Being Diagnosed With Cancer?

my sister has fuild around her heart,shes 73yrs old with cancer on her limp nohys under the armpits and down by her kidney side. her doctor says the one cancer is active and the other just lying domain,but they are worried about her fuild up.but she tell us that they want to do surgery to check what causes it.my question is how long and can live without medical attention?