Misclassification of cause of death in cancer patients

July 16, 2002

The overall cancer mortality rate could increase by about 1% if all deaths within 1 month of cancer-related surgery were correctly attributed to the underlying cancer rather than the surgical procedure, suggests new research appearing in the July 17 issue of the Journal of the National Cancer Institute.

In making judgments about the progress against cancer, deaths from treatment and diagnosis must also be accounted for, conclude study authors H. Gilbert Welch, M.D., and William C. Black, M.D., of Dartmouth Medical School.

The calculation of cancer mortality depends on the accurate determination of the underlying cause of death. Welch and Black argue that cancer mortality should include deaths from treatment for cancer as well as deaths from the disease. They note, however, that clear guidelines for classifying treatment-related deaths in cancer do not exist.

As a rule, researchers consider deaths within 30 days of a surgical procedure to be treatment-related when calculating mortality from the underlying disease.

To determine if this rule is being applied uniformly to cancer patients, Welch and Black used national cancer registry data to find out the reported cause of death in patients who, between 1994 and 1998, died within 1 month of cancer-related surgery to remove a solid tumor. Among the 4,135 deaths within 1 month of diagnosis and cancer-related surgery, 41% were attributed to a cause other than the cancer. The proportion of cases not attributed to cancer ranged from 13% for cervical cancer to 81% for laryngeal cancer. The authors note that there is a trend toward increasing misclassification among those cancers, such as breast and prostate, in which early detection has increased substantially.

If all deaths within 1 month of cancer-directed surgery were attributed to cancer, cancer mortality would rise by about 1% over current estimates in national trends, they authors say. They note that the proportion of deaths not attributed to cancer was highest during the period immediately following surgery. If all deaths in the year following cancer-directed surgery were attributed to cancer, then, according to the authors, the reported cancer mortality would increase from 2% to 4%.

The authors conclude that some deaths resulting from cancer-related surgery are not being properly attributed to cancer. "Although the estimated effect of this misclassification on overall cancer mortality is modest, it may be indicative of more widespread confusion about how to code treatment-related deaths of patients with cancer," they write.

The authors propose developing some rules under which all deaths within 1 month of surgery, radiation therapy, or chemotherapy are attributed to the cancer for which the treatments were initiated.

In an accompanying editorial, Colin B. Begg, Ph.D., and Deborah Schrag, M.D., of the Memorial Sloan-Kettering Cancer Center in New York, caution that the proposed changes in classifying cancer-related deaths may introduce inaccuracies. They note that deaths do occur suddenly and unpredictably, especially among older patients. Moreover, many deaths have multiple causes, and attributing death to one disease does not recognize the complexity of the issue.

Begg and Schrag conclude that "in view of the fact that the science of nosology (the determination of cause of death) is unlikely to ever be perfected, cause-specific mortality estimates must always be interpreted with caution in the context of related statistics on disease incidence and relative survival."
Contact: Hali Wickner, Dartmouth Medical School, (603) 650-1492, fax (603) 650-1730; DMS.communications@dartmouth.edu

Editorial: Christine Hickey, Memorial Sloan-Kettering Cancer Center, (212) 639-3573, fax (212) 639-3576, publicaffairs@mskcc.org.

Welch G, Black C. Are deaths within 1 month of cancer-directed surgery attributed to cancer? J Natl Cancer Inst 2002;94:1066-70.

Begg C, Schrag D. Attribution of deaths following cancer surgery. J Natl Cancer Inst 2002;94:1044-5.

Attribution to the Journal of the National Cancer Institute is requested in all news coverage.

Journal of the National Cancer Institute

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