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Early diagnosis and survival of breast cancer varies by race, WCH research finds

A new breast cancer study found that likelihood of being diagnosed at an early stage, and also survival rates after a stage I diagnosis, varied by race and ethnicity.

Black women were significantly less likely than white women to be diagnosed at stage I, while Japanese women were significantly more likely to get an early diagnosis. Black women also had the lowest seven-year survival rates following a stage I diagnosis.

Biological factors, such as the type of cancer, were responsible for much of these differences.

Early diagnosis is important because survival rates are very high for women diagnosed with breast cancer in its early stages.  

The research team from Women’s College Hospital in Toronto, led by Dr. Javaid Iqbal and Dr. Steven Narod, director of the Familial Breast Cancer Research Unit at Women's College Research Institute, used data on 373,563 U.S. women who were diagnosed with breast cancer from 2004 to 2011. The women were followed for an average of 3.4 years. Seventy-two per cent of the women were non-Hispanic white, 10 per cent were black, nine per cent were Hispanic white, seven per cent were Asian and two per cent were other ethnicities.

Almost half (48 per cent) of the women were diagnosed at stage I. However, there were significant differences:

  • In the largest group – non-Hispanic white women – 51 per cent were diagnosed at stage I.
  • Japanese women were most likely to be diagnosed at stage I (56 per cent).
  • Black women were least likely to be diagnosed at stage I (37 per cent).
  • Hispanic white women and South Asian women were also less likely to get a stage I diagnosis (40 per cent in each group).

Among women who were diagnosed at stage I, there were also significant differences in survival rates. The overall seven-year actuarial breast cancer survival rate for all the women in the study was 96.8 per cent. Survival rates were highest among Japanese women (98.6 per cent) and Chinese women (98.2 per cent). Survival rates were lowest among black women, who had a 93.9 per cent survival rate. Non-Hispanic white women had a 97 per cent survival rate, and Hispanic women 96.5 per cent.

The researchers calculated that the risk of dying of breast cancer that was diagnosed at stage I was 6.2 per cent in black women, compared to three per cent in non-Hispanic white women.

Biological differences in types of cancer and in the aggressiveness of tumours accounted for much of these differences. The likelihood of having a tumour that was aggressive despite being small size (less than two centimeters) was significantly higher in black women. The highest rates of small tumours that were found to have already spread to lymph nodes, that were advanced cancers, or that were triple-negative cancers was highest in black women.

While survival rates were linked to these biological factors, the researchers note that other factors may also play a role. Socioeconomic status, access to healthcare, use of healthcare, treatment adherence and other co-existing health conditions may also contribute to differences in breast cancer outcomes.

The study was published in Journal of the American Medical Association on Jan. 13, 2015.

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  • A publication of:
  • Women's College Hospital