Black women represented just under 10 percent of the 208,587 uterine cancer cases diagnosed in the United States between 2000 and 2017, but they made up almost 18 percent of the nearly 16,797 uterine cancer deaths during that period, Dr. Clarke’s study found.

The uterine cancer death rate for Black women is 31.4 per 100,000 women ages 40 and up, compared with 15.2 per 100,000 for white women in the same age group, Dr. Clarke reported. (Comparable death rates for Asian American women were nine per 100,000, and for Hispanic Americans, 12.3 per 100,000.)

That makes uterine cancer an outlier, since progress has been made toward narrowing the racial gap in death rates from most cancers over the past two decades. Another National Cancer Institute report, published in JAMA Oncology in May, found that overall, death rates from cancer have declined steadily among Black Americans between 1999 and 2019, though they continue to be higher than those of other racial and ethnic groups.

The reasons for the increase in uterine cancer cases are not well understood. The most common form, endometrioid cancer, is associated with estrogen exposure, which is higher when obesity is present, and obesity rates have been rising in the United States.

But non-endometrioid cancer has increased in prevalence, too, and it is not linked to excess weight. Dr. Clarke’s study found that Black women are more likely to have this aggressive form of uterine cancer. They are less likely to be diagnosed early in the course of the illness, and their survival rates are worse no matter when they are diagnosed and what subtype of the cancer they have.

“At every stage of diagnosis, there are different outcomes,” said Dr. Karen Knudsen, chief executive of the American Cancer Society. “Are they getting access to the same quality of cancer care?” She has called for more research into the factors driving the trends.