Survival, healthcare resource use and costs among stage IV ER + breast cancer patients not receiving HER2 targeted therapy: a retrospective analysis of linked SEER-Medicare data

BACKGROUND: Few studies have evaluated survival, treatment, resource use, and costs among women with stage IV ER + breast cancer (BC) who did not receive HER2 targeted therapy. METHODS: Using linked Surveillance, Epidemiology, and End Results (SEER) and Medicare data from 2006-2009, women aged 66+ years with an incident diagnosis of stage IV ER + BC (index date) in 2007 and no HER2 targeted therapy were identified. A comparison cohort without cancer was created from the SEER 5% Medicare sample and matched 1:1 to the study cohort based on age, sex, and race. All patients had continuous enrollment for a 12-month baseline period prior to index and were followed until the end of the study window, disenrollment, or death, whichever came first. Resource utilization and costs (by place of service, reported per patient per month, PPPM) were compared across cohorts. Treatment patterns including receipt of surgery, radiation, chemotherapy, aromatase inhibitors (AI), and non-AI hormonal therapy were evaluated for study cohort patients with at least 2 months of follow-up. Kaplan-Meier survival analysis was also conducted. RESULTS: 325 women with stage IV ER + BC without HER2 targeted therapy were identified and matched to 325 women without cancer. Mean age was 77 years for both cohorts, with average follow-up of 18 months for study patients and 26 months for comparison patients. Compared to the comparison cohort, study patients had significantly higher mortality (60.3% versus 31.1%, P < 0.001), shorter survival (survival at 36 months 28% vs. 62%) and higher resource utilization across all settings except for oral prescription drugs. Total PPPM healthcare costs were also significantly higher among study patients ($7,271 vs. $1,778, P < 0.001). Approximately 57% of study patients with 2+ months of follow-up received chemotherapy and over 62% received an AI during follow-up. Within 4 months of cancer diagnosis, surgery and radiation were received by 39% and 32% of study patients, respectively. CONCLUSIONS: We found significant excess clinical and economic burden among women with stage IV ER + breast cancer who did not receive HER2 targeted therapy. Future studies with more precise and recent data are warranted to confirm and extend these results.