DESTINY-Breast03
The head-to-head ADC trial where Enhertu beat Kadcyla by a wide margin, showing that payload and bystander effect matter.
PFS HR 0.33 (28.8 vs 6.8 months); OS HR 0.64. Redefined second-line HER2+ therapy and validated the DXd platform.
- Median 28.8 vs 6.8 months with Trastuzumab deruxtecan compared with Trastuzumab emtansine; about 22 months longer for half the group.
- A median is a midpoint: half the people did better than this and half did worse, so it is not a prediction for any one person.
- Put another way, the treated group had about 67 percent lower chance of the event at any given time (hazard ratio 0.33, likely range 0.26 to 0.43).
- This is a surrogate endpoint: it measures the cancer being controlled or absent on scans and tests, which often, but not always, translates into living longer.
- Median 52.6 vs 42.7 months with Trastuzumab deruxtecan compared with Trastuzumab emtansine; about 9.9 months longer for half the group.
- A median is a midpoint: half the people did better than this and half did worse, so it is not a prediction for any one person.
- Put another way, the treated group had about 27 percent lower chance of the event at any given time (hazard ratio 0.73, likely range 0.56 to 0.94).
- Overall survival counts deaths from any cause, so it is the most direct measure of whether a treatment helps people live longer.
- 78.5 vs 35 out of 100 had their tumour shrink with Trastuzumab deruxtecan compared with Trastuzumab emtansine; 43.5 more per 100.
- Roughly one extra person helped for every 2 treated. That is a rough figure taken from the two percentages, not a guarantee for any one person.
- A response rate counts how many people had their tumours shrink by a set amount; shrinking is encouraging but does not by itself show that people live longer or feel better.
- These results apply to the people the trial enrolled: HER2+ metastatic breast cancer after trastuzumab and taxane: T-DXd vs T-DM1. People in a different situation may not see the same effect.
- The trial selected people by a biomarker (HER2); the result should not be assumed for people whose cancer does not have it.
Numbers are from the trial as recorded here; see the source links in the table below. This is orientation, not medical advice: ask your team how closely the trial population matches you.
524 participants enrolled.
| Endpoint | Arm | n | Value | HR (95% CI) | p | Source |
|---|---|---|---|---|---|---|
| Progression-free survival (BICR)primary | Trastuzumab deruxtecan | 261 | 28.8 months | 0.33 (0.26–0.43) | <0.0001 | link |
| Trastuzumab emtansine | 263 | 6.8 months | ||||
| Overall survival | Trastuzumab deruxtecan | — | 52.6 months | 0.73 (0.56–0.94) | — | link |
| Trastuzumab emtansine | — | 42.7 months | ||||
| Objective response rate | Trastuzumab deruxtecan | — | 78.5% | — | — | link |
| Trastuzumab emtansine | — | 35% |
For HER2-positive metastatic breast cancer that has progressed after trastuzumab and a taxane, trastuzumab deruxtecan is now the standard second-line treatment and T-DM1 has moved later in the sequence. The benefit is large enough that ADC design, not just the target, is understood to be what matters. Patients need lung monitoring because of the risk of pneumonitis.
HER2-positive breast cancer is now routinely treated before surgery so that the pathology result can guide what comes after: patients with no residual cancer continue trastuzumab (with or without pertuzumab), while those with residual disease switch to T-DM1. This model of using the tumour's response as a test has since been copied in triple-negative and other cancers.