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Racial Disparities in Breast Cancer Mortality Rates

Black women who have breast cancer are more likely to die than white women. This was thought to happen due a factor in breast cancer called estrogen receptor status. But a new study conducted by the National Institutes of Health (NIH) revealed that other factors, not estrogen receptor status, are responsible for the differences in mortality rates.

Although there has been improvement in breast cancer care in recent years, disparities between white women and black women still remain. Black women are experiencing higher breast cancer mortality rates, even though breast cancer incidence in them has decreased.

Estrogen reception
There are two types of tumors which may develop in women with breast cancer. Only one kind of tumor is found in a breast cancer victim.

Estrogen receptor-positive (ER+) tumor: This type of tumor grows when exposed to estrogen. But this type also responds well to drugs such as tamoxifen, thus helping in treating cancer.

Estrogen receptor-negative (ER-) tumor: This type does not react to increase or decrease in estrogen. But it also does not respond to drugs, and thus is more difficult to treat.

Earlier, it was thought that difference in the prevalence of ER+ and ER- tumors is the main factor behind breast cancer mortality rates. But this has been refuted by the new study.

The study
The study has been conducted by the National Cancer Institute (NCI) of the NIH. They used data from the NCI’s Surveillance, Epidemiology and End Result (SEER) Program.

The researchers used statistical techniques to evaluate ratios of disparities between white and black breast cancer patients based on incidence, mortality and hazard rate (possibility of death), sub comparing with ER status. Doing this, the researchers were able to compare trends across all sub-groups equally.

It was found that, from 1990 to 2004, black-to-white breast cancer incidence ratios were stable, but mortality ratios increased over the years. That is, more black women who had breast cancer died than white women. This was the result even after adjusting for age at diagnosis, year of diagnosis, grade and stage of the tumor, socioeconomic status and ER status.

The study used an approach called the counterfactual approach. In this, it was estimated what the result would be if the population composition was different. Specifically, what if the proportion of ER+ and ER- tumors was equal in both populations, as well as similar hazard rate proportions.

This approach confirmed that higher mortality rates in blacks were not due to estrogen status, but due to hazard rates.

Another important finding of this study was that the higher mortality rates in black breast cancer patients occurred due to outcomes in the first three years of diagnosis. That is, things that happen to a black breast cancer patient in three years after diagnosis, whatever they are, result in their higher risk of mortality.

How the study can help
Though the study itself could not pinpoint the exact reasons for the disparities in mortality rates, it will help clinicians and other researchers. The study has shown that to reduce the disparity, the outcomes in the first 3 years after diagnosis of breast cancer in black women need to be addressed.

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