Doctors should not tell cancer patients how long they have to live - as their prognoses are usually wrong, medics say.

Researchers said that giving patients with advanced disease just one estimate, such as telling them they have 12 months to live, was only accurate around 20 to 30 per cent of the time.

Instead of such estimates, based on averages, medics should provide a range of estimates - including best and worst case scenarios, a medical conference has heard.

Dr Belinda Kiely, medical oncologist and senior research fellow at the University of Sydney, Australia, said medics worried about what to say to patients, without destroying hope.

She said doctors should give patients with advanced disease plenty of information, but not pin down a prognosis to any one estimate.

Her research found that women facing advanced breast cancer found it most helpful if they were given a best-case, worst case and typical survival.

Speaking at the Advanced Breast Cancer Fifth International Consensus Conference in Lisbon, she said: “Every week in my clinic, I meet women of all ages with advanced breast cancer and they frequently ask: ‘How long have I got?’ They have very practical concerns and questions that they want help with; for example, they might want to know whether they should cancel a planned holiday, whether they will be able to attend their daughter’s wedding, or whether they should stop working or sell their house.