Kidney cancers can be cystic, and differentiating between a single benign cyst of the kidney and a kidney cancer can occasionally be a problem. When many cysts are present, as in polycystic renal disease, the distinction is easier. Cysts may also be caused by some parasitic infections.
It will actually collect the oxygen in the ambient air (~21%) and convert it into a concentration of around 85-94%. One of the main reasons you would want a concentrator over a tank and regulator would be when you are using a lot of oxygen for taking ozone saunas or ozonating oils.
The permanent gases in air we exhale are roughly 78 per cent nitrogen, 15 to 18 per cent oxygen (we retain only a small amount), 4 to 5 per cent carbon dioxide and 0.96 per cent argon, the CO2 being of course used by plants during photosynthesis.