1. Generally, fluid retention like you mention is caused by kidney compromise and/or heart compromise (if the heart is not pumping strongly enough, there's not enough 'flow' through the kidneys for them to function adequately), and/or the blood is too "thick" (many times due to dehydration --- vicious circle, we see fluid retention so we drink less water = thicker blood = more edema/fluid retention).
So focusing on *always* full hydration plus kidney & heart programs should be a good place to start.
2. Swelling or water / fluid retention with cancer patients in advance stage is a common problem, lymphatic cleans is what always help.
For more details, please check the link from: