Are deaths within 1 month of cancer-directed surgery attributed to cancer?

Cancer mortality should include not only deaths from cancer but also deaths from cancer treatment. By convention, deaths within 30 days of a surgical procedure are considered treatment-related deaths in the calculation of operative mortality-that is, the chance of dying from surgery. How cause of death is attributed in patients who die within 1 month of cancer-directed surgery is unknown.

The National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) program data from 1994 through 1998 were used to examine the cause of death in patients diagnosed with one of 19 common solid tumors who had died within 1 month of diagnosis and had also received cancer-directed surgery. We determined the proportion of deaths not attributed to the cancer and the magnitude of the undercount in cancer-specific mortality.

Among 4135 patients with only one cancer who died within 1 month of diagnosis and cancer-directed surgery, the proportion of deaths not attributed to the coded cancer was 41% (1714/4135), ranging from 13% (1/8) for cervical cancer to 81% (13/16) for laryngeal cancer. Selected intermediate values include 25% (14/56) for esophageal cancer, 34% (177/525) for lung cancer, 42% (719/1695) for colorectal cancer, 59% (110/186) for breast cancer, and 75% (80/106) for prostate cancer. Restricting the analysis to deaths following specific major procedures (e.g., esophagectomy, pneumonectomy, colectomy) had little effect on the findings. If all deaths within 1 month of cancer-directed surgery were attributed to cancer, cancer mortality would rise about 1%.

Some deaths that are conventionally attributed to surgery are not being attributed to the cancer for which the surgery was performed. 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.