Young black women in the UK are more likely than their white counterparts to develop "worse" breast cancer with a poorer prognosis, research suggests.

This group has larger, more aggressive tumours with a higher risk of recurrence.

This is despite having the same access to treatment, the study in the British Journal of Cancer shows.

As yet unidentified biological factors may be to blame, say the Cancer Research UK investigators.

Such women might respond less well to breast cancer drugs like tamoxifen because of the genetic make-up of their tumour, they say.

The research team, based at the University of Southampton, looked at data from nearly 3,000 UK women - of whom 118 were black - who were younger than 40 when they were diagnosed with breast cancer.

Even when individual differences such as body weight and treatment variations such as availability of chemotherapy were taken into account, black ethnicity remained an independent indicator of poor prognosis.

Dr Ellen Copson and colleagues say there have been similar findings in the US, suggesting this could be an international trend, but further research is needed to try to pin down the exact cause or causes.

Early diagnosis may also play a role if black women are less aware of the symptoms or less "breast aware", and so less likely to identify worrying changes, they say.

This could mean their cancer is diagnosed at a later stage which would reduce the chance of successful treatment and recovery.

Although NHS treatment is designed to be equal for all, some cultural factors such as recent immigration to the UK or language barriers may in practice affect use of health services, they say.

Dr Julie Sharp, Cancer Research UK's head of health information, said: "It's worrying that ethnic background may be a factor influencing a woman's chance of surviving breast cancer. We know that some ethnic populations carry higher genetic risks of getting certain types of breast cancer, but if this difference is down to symptom awareness or access to healthcare, that is particularly concerning.

"More research is needed to look into the reason why young black women have higher rates of recurrence, but in the meantime women of any ethnic background should be aware of what is normal for their breasts and get any new lumps or anything unusual checked out by their GP. More often than not breast changes won't mean cancer, but it's best to get any unusual changes checked out."