Strengths and pitfalls of NNT and NNH in early breast cancer escalation trials.
Buonaiuto Roberto, Mangiacotti Federica Pia, Giudici Fabiola, Tafuro Margherita, Scarfetta Roberta, Longobardi Alessandra, Pagliuca Martina, Caltavituro Aldo, Arecco Luca, de Azambuja Evandro, Giuliano Mario, Arpino Grazia, Del Mastro Lucia, De Angelis Carmine, De Laurentiis Michelino, Puglisi Fabio
Breast (Edinburgh, Scotland) · 2026 · PMID 42285001
BACKGROUND: The management of patients with high-risk early breast cancer (eBC) requires balancing between clinical benefit and toxicity. Number Needed to Treat (NNT) and Number Needed to Harm (NNH) may provide a clinically intuitive framework to assess benefit-risk profiles, but their use in eBC has not been systematically explored.
METHODS: We analysed 10 phase II-III randomized clinical trials (RCTs) of treatment escalation strategies in patients with mid to high-risk eBC. To ensure consistency and cross-trial comparison, invasive disease-free survival (IDFS), disease-free survival (DFS), event-free survival (EFS), and overall survival (OS) were extracted at 3 and 5 years (y). Safety outcomes included any-grade (G) and G ≥ 3 adverse events (AEs), G5 AEs, and treatment discontinuation (TD). Absolute risk reduction (ARR) and absolute risk increase (ARI) were used to calculate NNT and NNH, respectively, reported with 95% CIs.
RESULTS: In patients with the HER2+ eBC, KATHERINE showed the most favorable efficacy, with NNTs of 9 and 8 for IDFS at 3 and 5 years, respectively, and a NNT of 27 for OS at 5 years. APHINITY reported the most favorable safety profile, with the highest NNHs for G ≥ 3 AEs (15) and TD (80). In patients with TNBC, CREATE-X reported the lowest NNTs for DFS (7 at both 3 and 5 years). The most favorable results in OS were observed in OlympiA (NNT 26) and KEYNOTE-522 (NNT 20). Regarding safety, KEYNOTE-522 achieved the most favorable NNH for G ≥ 3 AEs (26), while OlympiA showed the best NNH for TD (16). In patients with HR+/HER2- eBC, OlympiA showed the strongest efficacy results, with the lowest NNTs for IDFS at 3 (10) and 5 years (9), as well as for OS at 5 years (26). The most favorable NNHs were reported for G ≥ 3 AEs in OlympiA (8) and for TD in monarchE (19).
CONCLUSION: NNT and NNH provide intuitive metrics to communicate benefit-risk trade-offs in high-risk eBC, although their variability across trials, subgroups, and timepoints requires cautious interpretation.