a micro chip to keep track of cancer

A microchip no bigger than a speck of dust could help to identify cancers that are likely to spread.
that chip works by spying on cancer cells deep inside a tumour and monitors their activitives to see if they are likely to metastasise( start spreading through the body) the chip then transmits its finding back to a computer so that doctors can start treatment.
the chip would be injected into a tumour ,where it would carry out its spying duties for several days or weeks.