Older women are less likely to have breast cancer surgery than those who are younger, research suggests.

Experts are unsure of the exact reasons, although they say the findings cannot solely be explained by older women also having other illnesses.They are conducting more research into whether patients choose not to have surgery or whether other factors - such as age discrimination in the NHS - play a role.

Researchers examined the records of more than 23,000 women with breast cancer diagnosed in the West Midlands, Yorkshire and the North East between 1997 and 2005. They found that overall surgery rates dropped off with age, while women who had other illnesses were less likely to have surgery. Even when other illnesses were taken into account, women who were older were less likely to have surgery.

More than 85% of women aged 65 to 70 had surgery, but this fell to 70% in those over 70 and 50% among women over 80. Older women from deprived economic areas were also less likely to have surgery.

The research comes after a report last week found older people are more likely to die of cancer because they receive less investigation of and treatment for their disease due to "age bias" in the NHS.

The King's Fund and Cancer Research UK report found older people experience delays in having their case referred to a specialist and are less likely to undergo surgery. They also have worse outcomes than younger patients.

The findings were presented at the National Cancer Intelligence Network (NCIN) conference in London.

Katrina Lavelle, lead study author from the University of Manchester, said: "Previous research has shown that older women are less likely to have surgery for breast cancer compared with younger patients. This research suggests that the presence of other illnesses, which we know increases with age, does not fully explain the difference in treatment between older and younger patients. The good news is that over the time period we looked at, the numbers of women over 65 having surgery did rise from 68% to 75%."

Care services minister Paul Burstow said: "Cancer patients, irrespective of their age, should expect to have the best chance of survival and get the best treatment on the NHS. However, as this research shows, this is not always the case. Age discrimination is not acceptable in a modern NHS.

"This is why, together with Macmillan and Age UK, we have launched 13 pilot sites around the country to tackle poor cancer survival rates among older people. These pilots will help us to deliver improved outcomes for older people with cancer by making sure that their needs are properly assessed and met."