I’m coming up on my eight-year cancer checkup in April, where I’m hoping they’ll tell me I have no new passengers aboard. But the idea that it could return later in some other form has always been in the back of my mind; How would I know it’s back until it’s too late to treat properly?

Researchers are discovering dormant tumour cells, also known as disseminated cancer cells, in association with breast, prostate, lung, colon and other cancers, and these cells are increasingly implicated in some metastatic cancers. An estimated 30% of people who have been successfully treated for cancer might harbour these cells, although unpublished work suggests they could be even more common.

There is a field of cancer research dedicated to finding out why it comes back and how it’s triggered, but it’s still early days and there don’t seem to be any clear answers yet.