Who is this trial for?
This trial was for adults with PD-L1-positive triple-negative breast cancer (TNBC) that had spread locally or to other parts of the body and had not yet been treated for advanced disease.
People in the trial had:
- Triple-negative breast cancer (TNBC) — breast cancer that lacks estrogen receptors, progesterone receptors, and HER2 overexpression, leaving fewer targeted treatment options.
- PD-L1 positive tumours — cancer that expresses a protein called PD-L1, which predicts benefit from immunotherapy.
- Locally advanced unresectable or metastatic disease that had not previously been treated with systemic therapy for the advanced setting.
What kind of trial is this?
This trial tested whether an antibody-drug conjugate (sacituzumab govitecan) could replace standard chemotherapy in first-line treatment for PD-L1-positive metastatic TNBC — while keeping pembrolizumab (immunotherapy) in both arms.
Background: why researchers asked this question
Triple-negative breast cancer is the most aggressive subtype of breast cancer. It lacks the hormonal targets that give other breast cancers more treatment options. In PD-L1-positive metastatic TNBC, the standard first-line treatment combined chemotherapy (a taxane or nab-paclitaxel) with pembrolizumab (immunotherapy), based on earlier KEYNOTE trials.
Sacituzumab govitecan (SG) had already proven effective in TNBC in later lines of treatment (in the ASCENT trial). It targets Trop-2 — a protein overexpressed on nearly all TNBC cells — delivering a potent toxin directly inside the cancer cell. Researchers asked: can SG replace the chemotherapy component in the standard first-line combination, keeping pembrolizumab in both arms, to improve how long the cancer is controlled?
The trial: what was tested and how
ASCENT-04 (also called KEYNOTE-D19) enrolled 443 people with PD-L1-positive locally advanced or metastatic TNBC who had not yet received treatment for advanced disease. They were randomly assigned 1:1 to:
- Sacituzumab govitecan + pembrolizumab (SG + pembro): the antibody-drug conjugate plus immunotherapy.
- Chemotherapy + pembrolizumab: a taxane or nab-paclitaxel (standard chemotherapy) plus pembrolizumab — the existing standard of care.
Importantly, pembrolizumab was given to both groups — the only difference was whether SG or standard chemotherapy was paired with it. The primary measure was progression-free survival (PFS) — how long before the cancer grew or the person died.
Results: what they found
SG + pembrolizumab kept the cancer controlled longer, and the responses it produced lasted nearly twice as long. Importantly, despite similar overall rates of serious side effects, far fewer people needed to stop SG compared to standard chemotherapy.
Sacituzumab govitecan + pembrolizumab vs chemotherapy + pembrolizumab
The cancer stayed controlled for nearly 3.5 months longer on average with SG — a 35% lower risk of cancer growing or of dying at any given point (HR 0.65).
Among people whose tumours shrank, the benefit lasted nearly twice as long with SG (16.5 vs 9.2 months). This is a clinically meaningful difference in a disease where response durability matters greatly.
Both groups had high response rates. The difference was modest (60% vs 53%), but those who responded to SG stayed in remission for far longer.
Far fewer people on SG had to permanently stop treatment because of side effects — about one third the rate of the chemotherapy group. Overall severity of side effects (grade 3 or higher) was similar between groups: 71% vs 70%.
Overall survival data have not yet shown a difference between the two groups, which is not unexpected given that patients in the chemotherapy arm were allowed to cross over to sacituzumab govitecan after their cancer progressed. An updated analysis presented as a late-breaking abstract at the 2026 ASCO Annual Meeting showed that PFS2 — the time from enrolment until the cancer grew again on the next line of treatment — was also longer in the SG group, suggesting the early advantage of SG carries forward even after patients move on to subsequent therapy.
Who qualifies as PD-L1 positive?
PD-L1 (programmed death-ligand 1) is a protein on tumour and immune cells. Higher levels of PD-L1 expression predict a better response to pembrolizumab (which blocks its checkpoint partner, PD-1). In this trial, all participants were PD-L1 positive — which is the group already recommended to receive pembrolizumab with first-line chemotherapy. Testing for PD-L1 status is now a standard part of workup for metastatic TNBC.
The bottom line
For PD-L1-positive metastatic TNBC, replacing standard chemotherapy with sacituzumab govitecan — while keeping pembrolizumab in both arms — extended the time before the cancer progressed and, strikingly, nearly doubled how long responses lasted (16.5 vs 9.2 months). Far fewer people needed to stop SG due to side effects compared to standard chemotherapy. Overall survival data are awaited, but the PFS and durability results are meaningful in this aggressive cancer subtype.
What this could mean for you
- PD-L1 testing is essential. This trial enrolled only PD-L1-positive patients. Testing is standard; ask your team about your result.
- Both arms had pembrolizumab. The question in this trial was whether SG could replace the chemotherapy component — not whether to use immunotherapy at all.
- Responses lasted longer. Even though more people didn’t respond initially (60% vs 53%), those who did respond to SG stayed in remission nearly twice as long on average.
- Better tolerability. Fewer people needed to permanently stop SG. Common SG-related side effects include diarrhoea, hair loss, fatigue, and low blood counts.
- Survival data pending. The key question of whether SG + pembro helps people live longer is still being followed.
An oncologist’s perspective
Triple-negative breast cancer is a dreaded cancer type. We have often felt helpless watching the cancer take its toll no matter what we do. Any incremental benefit to survival is desperately needed, and seeing the promising results of a combination of two new cancer therapies — antibody-drug conjugates with checkpoint inhibitor therapy — is encouraging indeed.
Questions & comments
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