New research shows that chances of dying from very early breast cancer are small but the disease is riskier for young women and blacks, the same disparities seen for more advanced cancer.

Death rates in the 20 years after diagnosis totaled about 3 percent for women whose breast cancer was confined to a milk duct. The death rates were twice as high for those younger than 35 at diagnosis and in blacks - but still lower than those with more common invasive breast cancer.

The findings will likely add to the debate over how to treat these early kinds of tumors that some have said should not even be considered a true cancer because they rarely spread.

The study authors analyzed U.S. government data on more than 100,000 women diagnosed from 1988 to 2011 with DCIS - ductal carcinoma in situ. Women were aged 54 on average at diagnosis.

Though low, the risk of dying from breast cancer was almost twice as high as the breast cancer rate in the general population of U.S. women, said Dr. Steven Narod, the lead author and a senior scientist at Women's College Research Institute in Toronto.

More than 900 women died of breast cancer during the study years. Some had developed invasive disease in either breast, but more than 500 deaths were in women never diagnosed with a second tumor or recurrence, meaning their DCIS had likely spread before they received treatment, Narod said.

The study was published Thursday in JAMA Oncology.

DCIS will be found in about 60,000 U.S. women this year, versus more than 230,000 women expected to be diagnosed with invasive breast cancer, the cancer society estimates. More women have been diagnosed with DCIS in recent years because of increased screening and better imaging techniques.

Standard DCIS treatment is lumpectomy followed by radiation, although some women choose to have the entire breast or even both breasts removed. The study found that radiation reduced chances for disease recurrence but didn't lower 20-year survival chances. That may lead some women to skip radiation, Narod said.

By contrast, the results may lead some young women and blacks to seek more aggressive treatment including chemotherapy, although that isn't usually recommended when the death rate is less than 10 percent, he said.

"These are tough choices," said Dr. Len Lichtenfeld, the American Cancer Society's deputy chief medical officer.

Women diagnosed with DCIS shouldn't panic, he said, because chances for being cured are good. Still, the study shows the disease can behave like invasive cancer and doctors should discuss rates for recurrence and death, and inform patients of all options, he said.

Dr. Richard Bleicher, a breast cancer expert at Fox Chase Cancer Center in Philadelphia, noted that the study lacked information that may have influenced women's outcomes, including whether younger women who died had genetic mutations that may have put them at risk.

A JAMA Oncology editorial says more research is needed to better understand the riskiest DCIS cases and to test treatment approaches that may reduce deaths.