OBJECTIVES: When assessing evidence transportability between two settings, individual patient-level data (IPD) are usually available in only one. As a result, researchers use matching-adjusted indirect comparison (MAIC) to perform population adjustment. The presence of IPD in both settings provides a valuable opportunity to evaluate the extent to which MAIC weighting preserves the results from using IPD-based inverse-odds weighting (IO).

METHODS: We conducted a transportability study to compare the overall survival of individuals with HER2+ metastatic breast cancer (mBC) in the UK and the US between 2014 to 2023. In this study, IPD from the UK were obtained from the ESTHER registry and represented the target population. IPD from the US came from an EHR-derived de-identified mBC database and represented the study population. We performed population adjustment using inverse odds weighting and MAIC after summarizing UK IPD into aggregated data (AD).

RESULTS: The US cohort consisted of 907 individuals with a median age of 61 years, while the UK cohort included 248 individuals with a median age of 57. The restricted mean survival time (RMST) at 60 months was as follows: 41.7 months (se: 1.3) for the UK cohort; 40.0 months (se: 0.7) for the unweighted US cohort; 41.5 months (se, 0.8) for the US cohort after IO; and 41.3 months (se: 1.1) for the US cohort after MAIC. Compared to the UK, the hazard ratio estimates were 1.06 (0.88, 1.27) for the unweighted US cohort; 0.98 (0.79, 1.20) IO-weighted US cohort, and 1.00 (0.79, 1.27) for MAIC-weighted US cohort.

CONCLUSIONS: The point estimates obtained from population adjustment using MAIC were similar to those from IO. However, as expected, the MAIC estimates showed slightly greater variability. These findings provide support for using aggregated data to assess evidence transportability when individual patient-level data are unavailable for people with HER2+ mBC.