DESTINY-Breast03 Phase 3 Study Results

Adjudicated Drug-Related ILD/Pneumonitis Any grade, n (%) Grade 1 Grade 2 Grade 3 Grade 4 Grade 5 Time to first onset, median (range), days Outcome of worst event, n (%) Fatal Not recovered/not resolved Ongoing Recovering/resolving Recovered/resolved with sequelae Recovered/resolved 10 Daiichi-Sankyo DESTINY-Breast03 T-DXd n = 257 T-DM1 n = 261 For this safety update: • Majority of adjudicated 28 (10.9) 5 (1.9) 7 (2.7) 4 (1.5) 19 (7.4) 1 (0.4) 2 (0.8) 0 0 0 0 0 • 181 (33-507) 289 (80-499) • 0 8 (28.6) 0 1 (20.0)a 0 0 2 (7.1) 0 2 (7.1) 16 (57.1) 0 4 (80.0) ILD/pneumonitis cases were low grade and no new grade 4 or 5 events occurred in either treatment arm One additional grade 2 adjudicated drug-related ILD/pneumonitis occurred The majority of events resolved with ongoing follow-up ILD, interstitial lung disease; T-DM1, trastuzumab emtansine; T-DXd, trastuzumab deruxtecan. aPatient had an event of pulmonary embolism that the investigator considered to be grade 5. This was initially reported as respiratory failure but subsequently updated to pulmonary embolism. The ILD adjudication committee adjudicated this event as drug-related grade 1 ILD/pneumonitis. The death was not evaluable for adjudication. The investigator recorded disease progression as the primary cause of death.1 1. Cortés J et al. N Engl J Med. 2022;386:1143-1154 (supplementary appendix). Safety update: Sept 7, 2021 ASCO 2022 #1000 Oral 34

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