Background: Cancer stage is critical for treatment planning and assessing disease prognosis. The percentage of unknown staged cancer cases varies considerably across state cancer registries; factors contributing to the variations in unknown stage have not been reported in the literature before. The purpose of this study was to examine whether these variations were influenced by demographic and/or clinical factors as well as the type of reporting facility.
Methods: Invasive colorectal, lung, female breast, and prostate cancers diagnosed between 2004 and 2007 were obtained from the North American Association of Central Cancer Registries (NAACCR); 47 population-based cancer registries in the United States were included. The unknown stage was based on Summary Stage 2000 codes derived from Collaborative Stage Version 1 (CSv1). Relative importance analysis was used to identify variables that were essential in predicting unknown stage. Using state central registries as analytical units, multiple linear regression was used to evaluate factors associated with the percentage of unknown stage by cancer site; potential outlier registries with a high percentage of unknown stage cases were identified using boxplots and standardized residuals.
Results: Overall, lung cancer had the highest percentage of unknown stage (8.3%) and prostate cancer had the largest variation of unknown stage among registries (0.6%-18.1%). The percentages of neoplasms not otherwise specified (NOS) histology, non-microscopic confirmation, and non-hospital reporting source were positively associated (p less than 0.05) with percentage of unknown stage for all studied cancer sites before adjustment. Variables that retained a positive association with unknown stage including all demographic and clinical variables, year of diagnosis, and type of reporting source were black race, metropolitan area less than 1 million population, histologies of neoplasms NOS or epithelial neoplasms NOS, diagnosis year 2005, and non-hospital reporting source for colorectal cancer; metropolitan area less than 1 million population, neoplasms NOS histology, and non-hospital reporting source for female breast; and diagnosis year 2005 and non-hospital reporting source for prostate. After adjustment, none of the predictors were significant for lung cancer. We observed 1 potential outlier registry each for colorectal, lung and female breast cancers.
Conclusions: Factors associated with unknown stage differ by cancer site; however, the type of reporting source is an important predictor of unknown stage for all cancers except lung after adjustment. Central registries with high percentage of unknown stage should be made aware of their data quality issue(s). As a result, these registries can investigate those factors and provide training to registrars to improve their cancer data quality.