Measurement of skeletal related events in SEER-Medicare: a comparison of claims-based methods.

Background: Skeletal related events (SREs) are common in men with metastatic prostate cancer (mPC). Various methods have been used to identify SREs from claims data. The objective of this study was to provide a framework for measuring SREs from claims and compare SRE prevalence and cumulative incidence estimates based on alternative approaches in men with mPC.
Methods: Several claims-based approaches for identifying SREs were developed and applied to data for men aged [greater than or equal to] 66 years newly diagnosed with mPC between 2000 and 2009 in the SEER-Medicare datasets and followed through 2010 or until censoring. Post-diagnosis SREs were identified using claims that indicated spinal cord compression (SCC), pathologic fracture (PF), surgery to bone (BS), or radiation (suggestive of bone palliative radiation, RAD). To measure SRE prevalence, two SRE definitions were created: 'base case' (most commonly used in the literature) and 'alternative' in which different claims were used to identify each type of SRE. To measure cumulative incidence, we used the 'base case' definition and applied three periods in which claims were clustered to episodes: 14-, 21-, and 28-day windows.
Results: Among 8997 mPC patients, 46 % experienced an SRE according to the 'base case' definition and 43 % patients experienced an SRE according to the 'alternative' definition. Varying the code definition from 'base case' to 'alternative' resulted in an 8 % increase in the overall SRE prevalence. Using the 21-day window, a total of 12,930 SRE episodes were observed during follow up. Varying the window length from 21 to 28 days resulted in an 8 % decrease in SRE cumulative incidence (RAD: 10 %, PF: 8 %, SCC: 6 %, BS: 0.2 %).
Conclusions: SRE prevalence was affected by the codes used, with PF being most impacted. The overall SRE cumulative incidence was affected by the window length used, with RAD being most affected. These results underscore the importance of the baseline definitions used to study claims data when attempting to understand relevant clinical events such as SREs in the real world setting.