There are around 450 avoidable deaths among women from deprived areas each year, a study suggests.
The excess deaths occur because women from poorer backgrounds tend to be diagnosed with breast cancer when the disease is more advanced, the study's authors said.
The inequality between rich and poor breast cancer patients could arise because women from lower income groups are less aware of the symptoms of the disease and are more reluctant to see their GP, the authors told the National Cancer Research Institute Cancer Conference in Liverpool.
The researchers, based at the Universities of Leicester and Cambridge, looked how advanced breast cancer was in over 20,000 women diagnosed between 2006-2010 using data from the National Cancer Registration Service.
They then calculated how many lives could be saved with five years of diagnosis if the stage at diagnosis for poorer women matched those of the most affluent women.
If these socio-economic differences were removed, the equivalent of around 450 lives would be saved in England every year, they said.
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"These avoidable deaths are not due to differences in the response to treatment, or the type of breast cancer," said Dr Gary Abel, statistician at the University of Cambridge and study author. "Rather, these are deaths that might be avoided if cancer was caught as early in women from deprived backgrounds as those from more affluent backgrounds.
"The reason for this inequality may be a combination of these women being less aware of breast cancer symptoms and a greater reluctance to see their GP."
Dr Julie Sharp, head of health information at Cancer Research UK, said: "Other research shows that women from deprived backgrounds are more likely to feel embarrassed or worried about going to their GP - but it's important for women to take that step as going to the GP promptly could make all the difference.
"All women should be aware of how their breasts normally look and feel because we know that early diagnosis is one of the most important factors in whether breast cancer treatment is effective."
Eluned Hughes, head of public health at Breakthrough Breast Cancer, said: "By focusing on improving early diagnosis, particularly in deprived areas, we can have most impact in stopping women dying from breast cancer. Around 1,000 women are still dying from breast cancer each month in the UK and we must continue our efforts to beat the disease - breast cancer is not yesterday's problem.
"Most cases of breast cancer are found by women noticing unusual changes in their breasts and visiting their GPs. The earlier breast cancer is found, the better the chance of beating it, so it is important women check regularly. Breakthrough Breast Cancer's simple TLC (Touch Look Check) message shows women what signs and symptoms they should look out for."