EARLY ANALYSES OF NEWLY APPROVED DRUGS MAY PRODUCE BIASED CONCLUSIONS

OBJECTIVES: Real-world health care data are increasingly used to study the effectiveness of interventions in large, heterogeneous patient populations. It is important to understand what biases could arise in the analysis of real-world data collected shortly after a new treatment is introduced, especially in the design of comparative effectiveness research. METHODS: This retrospective cohort study used pharmacy and medical claims from the HealthCore Integrated Research Database. Eligible patients were age 18 years or older with a diagnosis of gastric or gastroesophageal junction cancer (GC) (ICD-9-CM code 151.xx) who received trastuzumab between January 1, 2010 and March 31, 2014. Patients were followed until censoring, death, or end of the data stream (July 31, 2014). Descriptive statistics were used to summarize trastuzumab use. Differences by year were evaluated using F-tests for continuous variables and X2 tests for categorical variables. RESULTS: The 188 eligible patients had a mean age of 60 years; 81% were male; 52% received radiation therapy, and 34% had a resection or gastrectomy. These factors were not significantly different by year of trastuzumab initiation. However, there were statistically significant differences (p