I think these machines will not be able to give 100% accurate result. In studies of this type there will always be errors. But even if this percentage of accuracy is high, then this will benefit humanity.
I'm not knowledgable enough to say if these machines will work fine or not.
I'm more thinking about the morality of the system. Imagine this machine tells you that you may have cancer on an airport.. before a very long flight ... what would go through your mind?
Hmm.... very good guess, I hadn't even thought of. But the test result is not a diagnosis. Only a number of clinical tests can accurately a final diagnosis.
I don't think it will directly tell you have cancer.
It may say, due your breath analyze you can have some problems in your lungs. See a doctor as soon as possible.
Now it is too soft, it would be like something between.