Societal and Healthcare Costs of Post-IDFS Events Following Adjuvant Ribociclib Plus an Aromatase Inhibitor (AI) Versus AI Alone in Pre- and Postmenopausal Women with Early HR+/HER2- Breast Cancer in Canada

Background: Recent advancements in early breast cancer (EBC) for high-risk populations have significantly improved invasive disease-free survival (IDFS). While cost-effectiveness has been assessed, the broader societal impact of improved IDFS remains unstudied. A non-homogeneous semi-Markov model was developed to estimate total healthcare and societal costs after first-line treatment with ribociclib plus an aromatase inhibitor (AI) or, alternatively, AI alone in patients with hormone-receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) EBC. Methods: Using an incidence-based approach, the model calculated total expected annual societal costs of disease-related events after cessation of adjuvant treatment with ribociclib plus AI or AI alone for HR+/HER2- EBC. The model includes five states: IDFS, non-metastatic recurrence (NMR), distant recurrence (DR), secondary primary malignancy (SPM) and death, with a one-year cycle length, and a new cohort entering each year. Health state transition probabilities are based on a previously published cost-effectiveness model (CEM). Costs are tallied only after IDFS (after cessation of adjuvant treatment) and include direct costs of medical care as well as indirect costs related to employment, productivity, and wage loss. Results: At the 4-year NATALEE data cut-off (April 2024), ribociclib plus AI reduced the risk of an IDFS event by 28.5% versus AI alone (HR 0.715), corresponding in the model to 23% fewer non-fatal events (NMR, DR, and SPM), 18% lower mortality, 23% lower total direct costs (−$957,471,465), and 24% lower indirect costs (−$448,542,692) from the period of cessation of adjuvant therapy until death. Healthcare savings were driven primarily by fewer distant recurrences and deaths, while societal savings were largely due to reduced caregiver costs. Conclusions: Treatments that reduce disease recurrence and mortality can significantly lower societal costs and alleviate burden on the healthcare system.