KEYNOTE-355
Established immunotherapy plus chemotherapy as first-line treatment for metastatic triple-negative breast cancer with PD-L1 expression.
OS 23.0 vs 16.1 months in PD-L1 CPS ≥10 (HR 0.73). No benefit in CPS <10, defining the PD-L1 threshold used today. Now being succeeded by ADC-based first-line regimens (ASCENT-04).
Setting
First-line metastatic TNBC: pembrolizumab + chemotherapy vs chemotherapy
Phase
Phase 3
Sponsor
Merck
Registry
Headline result
OS HR 0.73 in CPS ≥10.
Reported
2020
Enrolled
847
Replication
Consistent direction with IMpassion130 (atezolizumab, PD-L1+); IMpassion131 was negative, so the PD-L1 CPS ≥10 population and the chemotherapy partner matter. Now being superseded by ADC + pembrolizumab (ASCENT-04).
In plain words
What these results mean for people, not percentages
Overall survival, PD-L1 CPS ≥10primarysurvival endpoint
- Median 23 vs 16.1 months with Pembrolizumab + chemotherapy compared with Placebo + chemotherapy; about 6.9 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 0.55 to 0.95).
- Overall survival counts deaths from any cause, so it is the most direct measure of whether a treatment helps people live longer.
Progression-free survival, PD-L1 CPS ≥10primarysurrogate endpoint
- Median 9.7 vs 5.6 months with Pembrolizumab + chemotherapy compared with Placebo + chemotherapy; about 4.1 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 34 percent lower chance of the event at any given time (hazard ratio 0.66, likely range 0.5 to 0.88).
- 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.
Overall survival, CPS ≥1survival endpoint
- Median 17.6 vs 16 months with Pembrolizumab + chemotherapy compared with Placebo + chemotherapy; about 1.6 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 14 percent lower chance of the event at any given time (hazard ratio 0.86, likely range 0.72 to 1.04).
- The likely range for the hazard ratio crosses 1, so the difference could be due to chance.
- Overall survival counts deaths from any cause, so it is the most direct measure of whether a treatment helps people live longer.
- Not significant.
Be careful
- These results apply to the people the trial enrolled: First-line metastatic TNBC: pembrolizumab + chemotherapy vs chemotherapy. People in a different situation may not see the same effect.
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.
847 participants enrolled.
Overall survival, PD-L1 CPS ≥10primary
HR 0.73 (0.55–0.95) · p = 0.0185
Pembrolizumab + chemotherapy
23 mo
Placebo + chemotherapy
16.1 mo
Progression-free survival, PD-L1 CPS ≥10primary
HR 0.66 (0.5–0.88)
Pembrolizumab + chemotherapy
9.7 mo
Placebo + chemotherapy
5.6 mo
Overall survival, CPS ≥1
HR 0.86 (0.72–1.04)
Pembrolizumab + chemotherapy
17.6 mo
Placebo + chemotherapy
16 mo
Not significant
Source| Endpoint | Arm | n | Value | HR (95% CI) | p | Source |
|---|---|---|---|---|---|---|
| Overall survival, PD-L1 CPS ≥10primary | Pembrolizumab + chemotherapy | 220 | 23 months | 0.73 (0.55–0.95) | 0.0185 | link |
| Placebo + chemotherapy | 103 | 16.1 months | ||||
| Progression-free survival, PD-L1 CPS ≥10primary | Pembrolizumab + chemotherapy | — | 9.7 months | 0.66 (0.5–0.88) | — | link |
| Placebo + chemotherapy | — | 5.6 months | ||||
| Overall survival, CPS ≥1 | Pembrolizumab + chemotherapy | — | 17.6 months | 0.86 (0.72–1.04) | — | link |
| Placebo + chemotherapy | — | 16 months |
Replication
Consistent direction with IMpassion130 (atezolizumab, PD-L1+); IMpassion131 was negative, so the PD-L1 CPS ≥10 population and the chemotherapy partner matter. Now being superseded by ADC + pembrolizumab (ASCENT-04).