A prevention or preventive measure is a way to avoid an injury, sickness, or disease in the first place, and generally it will not help someone who is already ill (though there are exceptions). For instance, many babies in developed countries are given a A treatment treats a problem, and may lead to its cure, but treatments often ameliorate a problem only for as long as the treatment is continued, especially in chronic diseases. For example, there is no cure for AIDS, but treatments are available to slow down the harm done by HIV and delay the fatality of the disease. Treatments don't always work. For example, chemotherapy is a treatment for some types of cancer. In some cases, chemotherapy may cause a cure, but not in all cases for all cancers. When nothing can be done to stop or improve a medical condition, beyond efforts to make the patient more comfortable, the condition is said to be untreatable. Some untreatable conditions naturally resolve on their own; others do not.
Cures are a subset of treatments that reverse illnesses completely or end medical problems permanently. Many diseases that cannot be cured are still treatable.