Statins, the cheap drugs taken by millions to protect against heart attacks, may help cut the death toll from cancer, according to two American studies.

The research, presented in Chicago at the world’s biggest cancer treatment conference, found statins increased women’s survival from common cancers such as breast, bowel and ovarian cancer by 40%. In bone cancer, the death rate was reduced by 55%. A second study showed that men with advanced prostate cancer taking statins were also 40% less likely to die than those who were not.

The two studies were observational – they looked back to see whether there was a difference in the death rate in a large group of people with cancer, some of whom had been taking statins and some of whom had not. They were not randomised controlled trials, considered the “gold standard” in drug research.

But Dr Ange Wang of the Stanford University School of Medicine, who led the women’s study, said the findings suggest statins could play an important part in cancer treatment. “We’re definitely very excited by these results,” she said.

Unlike aspirin, which research has shown can help prevent cancers, statins did not have a protective effect among those who took them – but once they had cancer, they were less likely to die from it.

Wang’s research came from the Women’s Health Initiative study, a cohort of 146,000 women who were enrolled between 1993 and 1998 in 40 centres in the US. The study has already provided answers to other questions, including the risks of hormone replacement therapy in breast cancer. More than 3,000 of the women have died of cancer. The researchers looked to see whether there were more women on statins among those who survived than those who died.

The women would have been prescribed statins by their doctors to prevent heart disease and strokes. One question will be whether these women would be less likely to die of cancer for other reasons, such as receiving better treatment and having their cancer picked up earlier. The researchers try to adjust for those and other differences.

The largest survival difference was for bone cancer, but that may be partly because it is a rarer form of the disease, so there will not have been so many women affected by it. Larger numbers are more convincing.

Wang agreed that the study did not prove statins were the reason why people were more likely to survive. More research was needed, she said. “I think it should be a priority given how common statins are and how much their use has expanded, and how prevalent cancer is.”

The second study looked into the effects of statins on survival from advanced prostate cancer – a disease where it is known statins can help.The Rutgers Cancer Institute of New Jersey looked back at the case notes of 20,000 men with high-risk prostate cancer to find out who among them had been on statins. Some had been on a combination of statin and metformin for type 2 diabetes as a result of obesity, another risk for prostate cancer. More than 1,300 of the men had died. Those taking statins were 43% less likely to die from the disease, they found.

Dr Richard Roope, GP adviser to Cancer Research UK, said: “This is interesting research but it doesn’t prove that post-menopausal women should take statins to lower their risk of dying from cancer.

“We don’t know for sure if the link shown between increased cancer survival and statin use is due to the drugs themselves or some other reason. More research is needed before we can say whether it would be beneficial for more women to take statins.”