A mum from Huntingdon who was told last August, she had only weeks to live because of cancer – and would never see her baby crawl – has gathered a group of more than 100 people to join her in running the Peterborough half marathon for charity in October.

Rebecca Griffiths, 33, known as Bex, a detective sergeant with Cambridgeshire police, was diagnosed with bowel and liver cancer when she was still on maternity leave. Her baby, Benjamin was seven months old and her older boy, William was five.

She decided that life just had to carry on. Despite undergoing chemotherapy, she went back to work and having run all her life, she kept on running. When she found that her tumour had shrunk, she put out the call for other people to run with her.

She said: "My husband, Jon (a police sergeant with the Metropolitan Police) asked how long we had. It meant I wouldn't see Benjamin's first birthday or ever hear him call my name. I wouldn't be able to play tooth fairy to William or see him get his 100m swimming badge. I told the doctor that I would fight the cancer and that I wasn't prepared to leave my boys."

Bex's mother, Ann, a modern matron at Papworth, had died of bowel and liver cancer five years earlier. Bex's bowel cancer turned out to be polyps which can be removed but she was told that the tumour on her liver was so huge that nothing could be done. "There was no liver left. It couldn't be worse," she said.

But after two courses of chemotherapy, doctors found that the tumour had shrunk dramatically after each one. Her liver has gone back to its normal size.

Bex, now on her third course, says she has not changed anything in her lifestyle, apart from drinking green tea and cranberry juice. She was never a smoker or a drinker, and has kept on running.

Nurse, Gini Melesi, from Huntingdon Community Cancer Network (HCCN), who treats Bex with her chemotherapy in her home, told The Hunts Post: "Research has shown that people who exercise have a better outcome than people who don't."

'Team Bex', raising money for HCCN by running the half marathon, has gone national and international. It includes nurses at Hinchingbrooke Hospital, head teacher Stephanie Baldwin and staff at William's School, Cromwell Academy, Bex and Jon's police colleagues and friends from Manchester, Devon, Oxford and Eastbourne.

In August, Bex's former police colleague, Claire Rennie, is planning to ride part of the Tour de France, from St Michel de Maurienne in the French Alps, up the Col du Télégraphe and then the Col du Galibier.

Two evenings a week, the Huntingdon contingent runs around the roads. On Saturday mornings, they run around Hinchingbrooke Park. Most of them are first-time runners. When she can't run, Bex goes with them on her bike to make sure they do their stretches.

Her tip for anyone who wants to start running is to run from one lamppost to the next, then jog to the next one, then run to the next one. Gradually, you increase the number of lampposts you can run. She taught her runners like that and now they can run five miles without stopping. She says: "They don't have to do this. It's great to see the smiles on their faces."

The runners are all sponsored to support HCCN, which works to help people through cancer and after recovery. The charity, which provides treatment in the patient's home, is hoping to open a centre, where people can exercise, and receive moral support.

HCCN says that after cancer, people's lives have often been shattered. Their relationships have changed. Their career may have stopped. There may be side effects and recurrences of the illness they are not prepared for. It provides nutritional advice and exercise classes and holds conferences twice a year.

INFORMATION: Signing up for the Peterborough Half Marathon costs £25. See www.perkinsgreateasternrun.co.uk. To join Bex's Runners, email her at team.bex2015@yahoo.com. To sponsor Bex, go to www.justgiving.com/rebecca-Griffiths4. For Claire Rennie, visit www.justgiving.com/Claire-Renni2.