Colon and rectal cancer death rates are now nearly 50 percent higher in blacks than in whites, according to American Cancer Society research being released Monday.
The gap has been growing since the mid-1970s, when colon cancer death rates for the two racial groups were nearly equal.
"We have seen this enormous progress in whites. We could be seeing the same progress in blacks, if we could overcome disparities in access to health care," said Elizabeth Ward, who oversees surveillance and health policy at the cancer society.
Colorectal cancer is the third leading cancer killer in the United States. About 50,000 Americans will die of the disease this year, the cancer society estimates.
Last month, researchers reported the rate of new cancers in general is inching down and death rates continue to decline in the United States - important good news in the fight against the dreaded disease.
But when it comes to colon cancer, progress has been greater for whites than for blacks, the new report says.
The rate of diagnoses in blacks was about 19 percent higher than it was for whites in 2005, the most recent year for which statistics are available.
The death rate difference was even more pronounced. Among blacks, there were about 25 deaths per 100,000 people, compared to 17 per 100,000 in whites - a 48 percent difference.
The two groups' death rates were similar until the 1980s when colon cancer began to kill blacks at a higher rate than whites.
Researchers say it's not clear why black mortality jumped in the 1980s, but it started a gap that continued to widen even after the black rate began to fall again.
Colon cancer deaths can be prevented by early diagnosis through screening and quality care. The screening rate for whites is 50 percent compared to just 40 percent for blacks.
The screening rate for Hispanics is an even-lower 32 percent, but the death rate for Hispanics - fewer than 13 per 100,000 - is lower than it is for whites.
That paradox is not unique to colon cancer: Poorly insured Hispanics have fared better than whites and blacks in several measures of cancer and heart disease.
"It's a mystery," said Dr. Daniel Blumenthal, chair of the Morehouse School of Medicine's Department of Community Health and Preventive Medicine.