Headaches are a very common ailment that most of the time are not a sign of something more serious. A lack of sleep, loud noise, brightness, even changing weather can cause a headache that, for the most part, can be cured with some rest or over-the-counter medicine.

What if doctors were able to identify, with a simple blood test, when a patient’s cancer was starting to make a return? Or that a person’s disease was so well treated it would not return?