ATLANTA  A nationwide study has found that the uninsured and those covered by Medicaid are more likely than those with private insurance to receive a diagnosis of cancer in late stages, often diminishing their chances of survival.

The study by researchers with the American Cancer Society also found that blacks had a higher risk of late diagnosis, even after accounting for their disproportionately high rates of being uninsured and underinsured. The study’s authors speculated that the disparity might be caused by a lack of health literacy and an inadequate supply of providers in minority communities. The study is to be published online Monday in The Lancet Oncology.

Previous studies have shown a correlation between insurance status and the stage of diagnosis for particular cancers. The new research is the first to examine a dozen major cancer types and to do so nationally with the most current data. It mined the National Cancer Data Base, which began collecting information about insurance in the late 1990s, to analyze 3.7 million patients who received diagnoses from 1998 to 2004.

The widest disparities were noted in cancers that could be detected early through standard screening or assessment of symptoms, like breast cancer, lung cancer, colon cancer and melanoma. For each, uninsured patients were two to three times more likely to be diagnosed in Stage III or Stage IV rather than Stage I. Smaller disparities were found for non-Hodgkins lymphoma and cancers of the bladder, kidney, prostate, thyroid, uterus, ovary and pancreas.