Breast cancer has been less common in black women than white women for decades. However, it kills black women at a much higher rate.

CBS News reports that the gap in breast cancer diagnoses has closed. A new report is showing that black and white women are now being diagnosed with breast cancer at the same rate. For black women, diagnoses of breast cancer has become more common, while the diagnosis for white women has leveled off.

The report was published by CA: A Cancer Journal for Clinicians. The research is based off of data in cancer registries in nine areas of the United States. The areas represent 9% of the entire nation.

In 2012, black and white women were diagnosed at nearly the same rate of 135 cases per 100,000 women. Ten years ago, white women were diagnosed at a rate of 132, and black women at 124.

Some believe that white women have had a higher number of diagnoses due to the choice to wait to have children. Studies have linked early childbirth to lower breast cancer risk, later on. Researchers are unsure why diagnoses have increased among black women.

An increase in screenings may play a part, while others strongly believe obesity is key. Obesity poses a higher cancer risk among older women, and obesity is on a dramatic rise among black women. Seven of the states with increased rates were in the Southern portion of the US, where obesity rates are above average.

The death rate for breast cancer has decreased for all women, which is likely due to early diagnosis and treatment. However, deaths among white women have been on the decline for a longer period, at a steeper rate.

Higher numbers of black women are diagnosed with the most aggressive of the three categories of breast cancer, triple negative. According a report last year, black women have almost double the rate of triple negative breast cancer than white women.