For the first time ever, scientists have precisely tracked down the spread of one patient's cancer, learning surprising new details about how some tumours quickly become deadly.

The worst news with a cancer diagnosis often come when doctors discover the tumour has metastasised - spread to other parts of the body, causing secondary tumours. It's extremely tricky to pin down the timing of metastasis, but such knowledge can really help doctors improve a patient's treatment options.

"Tracking, or even better predicting, a cancer's behaviour will be key to planning new treatment strategies that target tumours with drugs at exactly the right time for maximum effect," says one of the researchers, Andrea Sottoriva from the Institute of Cancer Research (ICR).

In this case, a team led by scientists from the ICR analysed the metastasis of bowel cancer in a patient who got an unlucky side effect from a diagnostic test.

As the disease progressed, that side effect meant doctors knew precisely when one of the man's secondary tumours had emerged, allowing for the most precise timeline of cancer development ever traced in a patient.

The man was first diagnosed with bowel cancer in 2008, and underwent surgery. But doctors also found a nodule in his lung, which they decided to keep an eye on in case it turned out to be cancerous.

In 2011, they biopsied the nodule using a common diagnostic technique - reaching in with a needle and extracting a sample for analysis. As suspected, it turned out to be a secondary tumour, and the patient received another surgery.

Unfortunately, the needle biopsy had also produced a rare side-effect called 'needle tract seeding', when cancerous cells extracted from the sample are left behind in the patient's tissue.

Two years later, doctors discovered another tumour in the man's chest wall, precisely where the biopsy had been done. He also had other metastases, but it was the cancer cells left behind by the needle that became the key for unlocking the whole case.

The scientists used that one tumour as a timestamp to calibrate against all other tumours in the patient's body. Using genetic analysis of cancer cell mutations paired with mathematical modelling, they built a complete timeline from the moment the cancer first emerged in the bowel.

"Our research was able not only to track the genetic evolution of the cancer, but also to put precise timings on each stage in a cancer's progression," says Sottoriva.

"The mathematical techniques we borrowed for our study were originally developed to measure the time when new species of plants and animals arose during evolution."

The unique timeline gave the team some really unexpected clues.

Normally it's thought that cancer lurks in the bowel for quite a while before making a break for it and travelling to other areas. And once that happens, the prognosis quickly becomes dire.

But in this case, the researchers were surprised to find that the cancer metastasised to the lung and thyroid within just a year of first emerging. And then, instead of spreading rapidly, the disease slowed right down - the patient was first diagnosed when he'd already lived with it for five to eight years.

"It suggests that sometimes, there's a large time window to make diagnosis early and disrupt metastatic spread," lead researcher Nicola Valeri from ICR told Andy Coghlan at New Scientist.

"It means there might be periods of years where we could intervene."

For this patient, unfortunately it was too late, and he died in 2015 from another new metastasis - this time in the kidneys. But he and his family granted the researchers full permission for publishing the results of the unique study.

The team also found some genetic clues in the patient's tumour which could explain why the disease progressed in such an unusual way. If we can better predict the spread of bowel cancer, we have a better shot of successfully treating it.

The study was published in Annals of Oncology.