Assessing the utility of cancer-registry-processed cause of death in calculating cancer-specific survival.

Abstract

Cancer registries use algorithms to process cause of death (COD) data from death certificates, but uncertainties remain regarding the accuracy and utility of those data in calculating cancer-specific survival (CSS). Because it is impractical to reconfirm the COD through meticulous review of the primary medical records, the observed cancer deaths could be compared with the number of attributed deaths, as estimated by using a relative survival (RS) approach, to determine utility in CSS estimation. Six major cancer types were evaluated using Surveillance, Epidemiology, and End Results (SEER) data (1988-1999 cohort). The COD utility was quantified by using the observed-to-expected ratio (O/E ratio) approach, which was calculated as the SEER-documented observed number of cancer-specific deaths divided by the number of expected deaths attributed to the malignancies as estimated using a RS approach. Favorable utility would have an O/E ratio close to 1. In total, 338,445 patients were identified; and their O/E ratios were 0.97, 0.98, 0.90, 1.07, 1.02, and 0.92 for breast, colorectal, lung, melanoma, prostate, and pancreas cancer, respectively. O/E ratios varied slightly with patients' age, race, and tumor stage, but not by sex. CSS for patients with lung cancer appeared to be overestimated considerably. Patients with multiple cancer diagnoses had poor O/E ratios compared with those who had only 1 cancer. The utility of COD in calculating CSS depended variously on the risk of cancer-related mortality and nontumor factors. However, the impact of this variation on CSS generally was small. The current results indicated that the COD assigned by cancer registries has acceptable validity, and CSS is considered an acceptable surrogate for RS in most circumstances.