I agree, but even with all the authorizations, it looks like a hard problem. You need like 20 persons with cancer. Before starting chemo? A matching group of 20 healthy persons. What about symptoms of cancer, like big moles in skin cancer or low weight in colon cancer?

Since the person with/without cancer know the situation, they may give involuntary hints. Just sedate them so they are sleeping while testing?

What if the person can detect some cancers and no others?