Background: Breast cancer is treated with many different modalities, including chemotherapy that can be given as a single agent or in combination. Patients often experience adverse events from chemotherapy during the cycles of treatment which can lead to economic burden.

Objective: The objective of this study was to evaluate costs related to chemotherapy-related adverse events in patients with metastatic breast cancer (mBC) in an integrated health care delivery system.

Methods: Patients with mBC newly initiated on chemotherapy were identified and the first infusion was defined as the index date. Patients were ≥18 years old at time of index date, had at least 6 months of health plan membership and drug eligibility prior to their index date. The chemotherapy adverse events were identified after the index date and during first line of chemotherapy. Episodes of care (EOC) were created using healthcare visits. Chart review was conducted to establish whether the adverse events were related to chemotherapy. Costs were calculated for each visit, including medications related to the adverse events, and aggregated to calculate the total EOC cost.

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Results: A total of 1,682 patients with mBC were identified after applying study criteria; 54% of these patients had one or more adverse events related to chemotherapy. After applying the EOC method, there were a total of 5,475 episodes (4,185 single episodes [76.4%] and 1,290 multiple episodes [23.6%]) related to chemotherapy-related adverse events. Within single episodes, hematological (1,387 EOC, 33.1%), musculoskeletal/pain related (1,070 EOC, 25.6%), and gastrointestinal (775 EOC, 18.5%) were the most frequent adverse events. Patients with adverse events related to single EOC with anemia and neutropenia had the highest total outpatient costs with 901 EOC ($81,991) and 187 EOC ($17,017); these patients also had highest total inpatient costs with 46 EOC ($542,798) and 16 EOC ($136,768). However, within multiple episodes, hematological (420 EOC, 32.6%), followed by infections/pyrexia (335 EOC, 25.9%) and gastrointestinal (278 EOC, 22.6%) were the most frequent adverse events.

Conclusion: The economic burden related to chemotherapy adverse events in patients with mBC is substantial.

Keywords: metastatic breast cancer, chemotherapy, adverse events, costs, health care use, economic burden