BACKGROUND: In an ongoing postauthorization drug safety study, the validity of algorithms to identify cancer outcomes among individuals with type 2 diabetes mellitus (T2DM) and taking an antidiabetic drug (AD) was evaluated as a pilot validation assessment in the United States (US) Medicare administrative claims database.
OBJECTIVES: To estimate the positive predictive values (PPV) of claims-based algorithms for female invasive breast cancer and in situ or invasive bladder cancer among individuals with T2DM in US Medicare.
METHODS: Patients were fee-for-service US Medicare enrollees aged ≥ 65 years initiating an AD drug (2014-2015). Algorithms included two recorded diagnoses of female invasive breast cancer (ICD-9-CM 174.* or ICD-10-CM C50.*; males excluded) or in situ or invasive bladder cancer (ICD-9-CM 233.7 or 188.* or ICD-10-CM D09.0 or C67.*) in any setting on separate days and within 60 days of each other. Patients with the following in the 180 days prior to study entry were excluded: breast biopsy (breast cancer cohort) or hematuria, cystoscopy/bladder biopsy, or urine cytology (bladder cancer cohort). Medical records were requested for 109 breast cancer and 87 bladder cancer algorithm-identified cases. Up to 50 received patient records were included in each outcome-specific validation sample for clinical review. Using abstracted medical record information and prespecified case definitions, adjudicators classified each algorithm-identified case as a confirmed case, a confirmed noncase, or a postreview provisional case (insufficient information to assign case status). PPVs and 95% confidence intervals (CI) were estimated as the proportion of confirmed cases: (1) among all cases in the validation sample (postreview provisional cases treated as false positives); (2) removing postreview provisional cases from the denominator.
RESULTS: We obtained 38.5% (breast cancer, n = 42) and 59.8% (bladder cancer, n = 52) of requested patient records. Validation samples included 42 breast cancer and 48 bladder cancer algorithm-identified cases, with 28 and 43 classified as confirmed cases, respectively. The PPV (95% CI) for the algorithms (1) including all cases and (2) excluding postreview provisional cases were: breast cancer (1) 66.7% (50.5%-80.4%), (2) 77.8% (60.8%-89.9%); bladder cancer (1) 89.6% (77.3%-96.5%), (2) 95.6% (84.9%-99.5%).
CONCLUSIONS: The algorithms applied in this pilot validation study have moderate validity for identifying female invasive breast cancer and high validity for identifying bladder cancer among older patients with T2DM and taking an AD drug in US Medicare.
