LAUSR

Purpose We estimated average medical costs due to metastatic breast cancer (mBC) among younger (aged 18–44), midlife (aged 45–64), and older women (aged 65 and older) by phase of care: initial, continuing, and terminal. Methods We used 2003–2014 North Carolina cancer registry data linked with administrative claims from public and private payers. We developed a claims-based algorithm to identify breast cancer patients who progressed to metastatic disease. We matched breast cancer patients (mBC and earlier stage) to non-cancer patients on age group, county of residence, and insurance plan. Outcomes were average monthly medical expenditures and expected medical expenditures by phase. We used regression to estimate excess costs attributed to mBC as the difference in mean payments between patients with mBC ( N  = 4806) and patients with each earlier-stage breast cancer (stage 1, stage 2, stage 3, and unknown stage; N  = 21,772) and non-cancer controls ( N  = 109,631) by treatment phase and age group. Results Adjusted monthly costs for women with mBC were significantly higher than for women with earlier-stage breast cancer and non-cancer controls for all age groups and treatment phases except the initial treatment among women with stage 3 breast cancer at diagnosis. The largest expected total costs were for women aged 18–44 with mBC during the continuing phase ($209,961 95% Confidence Interval $165,736–254,186). Conclusions We found substantial excess costs for mBC among younger women and during the continuing and terminal phases of survivorship. It is important to assess whether this care is high value for these women.