Untreated - Not being cured,
left alone.
Untreated is mainly used in the medical context, when a certain health risk goes either unnoticed, or, just not treated. This can happen mostly because the patient is in denial, when one finds out he has testicular cancer they're not going to be jumping for joy, so they might deny it, and the problem gets worse.
If you ever feel that you have ANY form of sickness, don't let it go untreated, the cost of a doctor is less than the cost of your life.