A team at the University of East Anglia and the Children's Hospital Boston, collaborating with Italian researchers, found that African and American women with African ancestry are more prone to develop breast cancer before menopause and to die of it than their white counterparts.

This racial clinical difference first emerged in the 1970s in US, with mammography starting to be applied.

For a long time, this was blamed on medical care.

Instead, the new research points that this is due to surgery in pre-menopausal women that relapses the cancer growth.

In African American women, the average age of breast cancer diagnosis was found to be 46, while for White American women is 57.

Dr Isaac Gukas, of the University of East Anglia's School of Medicine, Health Policy and Practice, one of the investigators of the new research found in a previous work that this age was 43 in the case of the Nigerian women compared to 64 for British ones.

In Nigeria, more than 70% of the cases were under 50, while in Britain this percentage was under 20%.

A 2005 study pointed that women operated for breast cancer before the menopause had a much higher percentage of relapse.

"Surgery to remove a primary tumor induces the formation of new blood vessels -known as angiogenesis. In pre-menopausal women who have high levels of estrogen and other hormones, this may encourage the growth of the tumor," said Gukas.

"Early detection, through mammography, is more effective in post-menopausal women, and more white women are diagnosed after the menopause. This could explain the disparity in mortality."

Gukas believes that surgery-induced angiogenesis can explain the high mortality at young ages and the low chances of surpassing the cancer of African women.

By now, the researchers do not know what induces the earlier establishment of the cancer in the African women.

"We do not intend to oversimplify this subject, but it seems clear that at least part of the phenomenon of widening mortality along racial lines could be attributed to surgery leading to accelerated tumor growth in pre-menopausal women," said Gukas.

"We have the data from epidemiology. Now we need further research to confirm these observations before we explore any necessary changes in practice. We do not have enough evidence to alter treatment at present and younger women should not be deterred from having surgery. But, if further studies confirm our hypothesis, we may need to give them appropriate chemotherapy, including angiogenesis inhibitors, beforehand to ensure the best outcome," he said.