Imputation of missing prostate cancer stage in English cancer registry data based on clinical assumptions

Background: Cancer stage can be missing in national cancer registry records. We explored whether missing prostate cancer stage can be imputed using specific clinical assumptions. Methods: Prostate cancer patients diagnosed between 2010 and 2013 were identified in English cancer registry data and linked to administrative hospital and mortality data (n = 139,807). Missing staging items were imputed based on specific assumptions: men with recorded N-stage but missing M-stage have no distant metastases (MO); low/intermediate-risk men with missing N- and/or M-stage have no nodal disease (NO) or metastases; and high-risk men with missing M-stage have no metastases. We tested these clinical assumptions by comparing 4year survival in men with the same recorded and imputed cancer stage. Mull-variable Cox regression was used to test the validity of the clinical assumptions and multiple imputation. Results: Survival was similar for men with recorded N-stage but missing M-stage and corresponding men with MO (89.5% vs 89.6%); for low/intermediate-risk men with missing M-stage and corresponding men with MO (92.0% vs 93.1%); and for low/intermediate-risk men with missing N-stage and corresponding men with NO (90.9% vs 93.7%). However, survival was different for high-risk men with missing M-stage and corresponding men with MO. Imputation based on clinical imputation performs as well as statistical multiple imputation. Conclusion: Specific clinical assumptions can be used to impute missing information on nodal involvement and distant metastases in some patients with prostate cancer.