It will be interesting to see how this progresses. As you said, false positives would certainly be a significant issue, and underlining that would be a question of liability.

If Google's scanner tells you that it has detected the formation of cancer in your body and is incorrect, putting someone through this could well be life altering in the short term.

Similarly, if you believe Google's scanner to be accurate and it fails to detect the formation of cancer, what then? If you get beyond the beneficial stages of early detection of this disease because your Google scanner tells you you're fine, how does that play out and who pays for it?

What if the device is compromised and someone can essentially have what they like reported to you?

Obviously I support any and all efforts to tackle cancer, but putting cancer detection into the hands of the end user has many potentially chaotic scenarios, and this is without mentioning the significant privacy issues that would surround such a device.