Worse breast cancer outcomes for women from poorer backgrounds are not due to late diagnosis alone

Although other studies have found that lower socioeconomic status is linked with women consulting their doctors at a later stage when their cancer is more advanced, this is the first study to show that there may be other factors at work that mean these women are more likely to die from their disease.

Dr Esther Bastiaannet, an epidemiologist at Leiden University Medical Centre (Leiden, The Netherlands), told the seventh European Breast Cancer Conference (EBCC7) in Barcelona that the study included 127,599 women who were diagnosed with breast cancer between 1995 and 2005 in The Netherlands. Data from these women were linked with data from the Netherlands Institute for Social Research, which keeps records of socioeconomic status by postcode.

Dr Bastiaannet and her colleagues found that not only was there an association between tumour size at diagnosis and socioeconomic status, but also, even after adjusting for factors such as age, grade and stage of the tumour, year of diagnosis and treatment, there was still a statistically significant association between survival and socioeconomic status. Women from the poorest backgrounds were a fifth more likely to die within ten years of diagnosis than women from the wealthiest backgrounds.

Both the overall survival (deaths due to any cause) and relative survival (the ratio between the survival from breast cancer when compared to the survival expected, based on the general population) declined with lower socioeconomic status. Ten years after diagnosis, overall survival was 65% for highest socioeconomic status patients versus 58% for lowest socioeconomic status patients; relative survival was 79% for the highest socioeconomic status patients, versus 74% for the lowest socioeconomic status patients.

"An increase of five percent in relative survival [from 74-79%] may look small, but these differences are significant to the prognosis of patients with breast cancer," said Dr Bastiaannet. "The differences were statistically significant, even after adjustment for age, year of diagnosis, grade and stage of the tumour and treatment. The increased risk of death for the lowest socioeconomic status group was a fifth higher when compared to the risk for the highest socioeconomic status group.

"We concluded that socioeconomic differences in The Netherlands were associated not only with tumour size at diagnosis and but also with long term survival. The more advanced cancer at diagnosis in patients with a lower socioeconomic status only partly explains their decreased survival after five and ten years. We think further research is needed to identify reasons for these disparities, with the hope of eliminating them in the future. In addition, socioeconomic status should be considered as a prognostic factor for breast cancer patients in The Netherlands."

She said this was the largest study in Europe to look at the association between socioeconomic status and survival and the first to describe the disparities at a national level in The Netherlands. "I think that it is possible to extrapolate our findings to other countries in Europe that have similar healthcare systems to The Netherlands where healthcare is at a high level and available to everyone."

At present, it is not known for certain what factors might be contributing to the higher risk of death from breast cancer among women from poorer backgrounds. "Lifestyle factors, such as smoking, may play a role," said Dr Bastiaannet. "Access to early detection, treatment that could be influenced by other health problems, and other, as yet, unknown factors all may be involved as well."

The researchers are planning to extend their research by comparing treatment according to tumour stage, and by investigating the factors that could influence the choice of treatment.