A PD-L1/VEGF antibody plus chemo shrank most tumours in a small TNBC trial

An experimental antibody that blocks two targets at once — the immune checkpoint PD-L1 and the blood-vessel growth factor VEGF-A — produced tumour responses in most patients when added to chemotherapy as a first treatment for advanced triple-negative breast cancer, in an early-phase trial published in The Lancet Oncology [s1]. The signal is encouraging. But the study was small, single-arm and run at hospitals in one country, so what it shows and what it cannot show need to be kept carefully apart.

The drug and the disease

Triple-negative breast cancer (TNBC) lacks the three receptors that most breast-cancer drugs target, which is why it is harder to treat and why chemotherapy has long been the backbone of care. Pumitamig is an investigational bispecific antibody designed to hit PD-L1 and VEGF-A together [s1]. The rationale is that releasing the immune brake while also choking off a tumour's blood supply might work better than either alone — a hypothesis this trial was built to probe, not to prove.

What the trial did

This was a single-arm, phase 1b/2 trial at ten hospitals and cancer centres in China [s1]. Eligible patients were adults aged 18 to 75 with unresectable, locally advanced or metastatic TNBC, in reasonable general health (an ECOG performance status of 1 or less) and with at least one measurable lesion [s1]. They received pumitamig at 20 mg/kg intravenously every two weeks plus nab-paclitaxel at 100 mg/m² on days 1, 8 and 15 of each 28-day cycle, continuing until the cancer progressed or side effects became unacceptable [s1]. A phase 1b safety run-in of six patients preceded the phase 2 expansion [s1]. The co-primary endpoints were the confirmed objective response rate — the share of patients whose tumours shrank by a defined amount — and safety [s1]. The trial is registered as NCT05918133 [s2].

Between 27 June 2022 and 15 March 2023, 42 patients were enrolled and treated, with a median duration of exposure of 9.0 months [s1]. All were Chinese women, with a median age of 53 years [s1].

What it found

At a median follow-up of 35.2 months, the confirmed objective response rate was 73.8% — 31 of the 42 patients — comprising one complete response and 30 partial responses [s1]. A response rate near three-quarters in first-line metastatic TNBC is a strong-looking number.

Side effects were in keeping with the known profiles of the two drugs [s1]. The most common severe (grade 3 or worse) treatment-related events were a drop in neutrophils (13 patients, 31%), a drop in white cells (11 patients, 26%), protein in the urine (six patients, 14%) and febrile neutropenia (five patients, 12%) [s1]. Nine patients (21%) had a total of 14 treatment-related serious adverse events [s1]. Treatment-related side effects led four patients (10%) to stop both drugs, three (7%) to stop nab-paclitaxel only and two (5%) to stop pumitamig only [s1]. There were no treatment-related deaths [s1].

How to read it

The central limit is in the design, not the result. This was a single-arm study: every patient got the combination, and there was no comparison group [s1]. Without a control arm you cannot know how much of that 73.8% reflects the new antibody rather than the chemotherapy it was added to, or the particular patients who enrolled. Response rate also measures tumour shrinkage, not how long people live or stay free of progression — the outcomes that ultimately decide a cancer drug's worth. Those were not the primary endpoints here.

Two further cautions. The trial was small (42 patients) and conducted entirely in China in a group that was all female and of one ethnicity, so how the results generalise to other populations is untested [s1]. And the study was funded by the drug's developer, Biotheus, part of the BioNTech group [s1] — not disqualifying, and routine at this stage, but a reason to wait for independent, randomised confirmation. The investigators themselves conclude only that the findings "warrant further clinical evaluation" in global phase 2 and 3 trials [s1].

What to watch

The meaningful test is a randomised trial that pits the combination against standard first-line chemotherapy and measures progression-free and overall survival, in a broader patient population. Until that exists, this is a promising early signal for a new class of two-in-one antibody — enough to justify larger trials, not enough to change practice [s1].

This article describes early clinical-trial results and is not medical advice. Decisions about cancer treatment are for patients and their treating oncologists.