BioNTech SE (BNTX) and Bristol Myers Squibb & Co. (BMY) released interim data Tuesday from a global Phase 2 trial that could offer real hope to patients facing one of the most aggressive forms of breast cancer. The trial tested pumitamig (BNT327/BMS986545) combined with chemotherapy in patients with locally advanced or metastatic triple-negative breast cancer, regardless of their PD-L1 expression levels.

The results look genuinely encouraging. The combination showed strong anti-tumor responses while maintaining a manageable safety profile across both first-line and second-line treatment settings. The data is being presented at the 2025 San Antonio Breast Cancer Symposium.

Why This Matters for Patients

"Triple-negative breast cancer is a highly aggressive disease with a poor prognosis and 5-year survival rate of just 15% in advanced stages. There remains an urgent need for new treatment options – particularly for patients with PD-L1 low or negative tumors (CPS<10), a subgroup for whom the current standard of care is chemotherapy alone and existing PD-(L)1 inhibitors have historically shown limited benefit," said Peter Schmid, M.D., Ph.D., Lead Investigator and Director of the Breast Cancer Centre at St. Bartholomew's Hospital, London, UK.

"The anti-tumor efficacy observed in this interim analysis is encouraging and supports the ongoing investigation of pumitamig in the Phase 3 ROSETTA BREAST-01 trial."

That PD-L1 distinction is crucial. Many current immunotherapy treatments work best in patients whose tumors express high levels of PD-L1, leaving those with low or negative expression facing chemotherapy as essentially their only option. This trial didn't discriminate based on PD-L1 levels, potentially opening doors for a broader patient population.

The Trial Design

The study tested pumitamig at two different dose levels combined with four different chemotherapy agents in first-line and second-line treatment settings. In Cohort 1, patients received pumitamig at either 15 or 20 mg/kg every two weeks plus nab-paclitaxel until their disease progressed or toxicity became unacceptable.

Cohort 2 used a flat-dose equivalent of 20 mg/kg combined with three different chemotherapy regimens: paclitaxel in Arm 1, gemcitabine plus carboplatin in Arm 2, and eribulin in Arm 3. The interim analysis included 74 patients as of the October 1, 2025 data cutoff.

The Numbers Look Good

Among 39 efficacy-evaluable patients in both first-line and second-line treatment (all from Cohort 1), the confirmed objective response rate hit 61.5%. The unconfirmed objective response rate reached 71.8%, and the disease control rate came in at an impressive 92.3%.

The progression-free survival rate at nine months was 59.3%. Median progression-free survival, median duration of response, and median overall survival weren't mature enough at the time of analysis to report, which makes sense given the relatively early stage of the data.

Perhaps equally important, pumitamig plus chemotherapy demonstrated a manageable safety profile across both cohorts and with all four chemotherapy combinations tested. Safety matters a lot when you're talking about combining multiple cancer treatments.

What Comes Next

The companies are already running a global randomized Phase 3 trial called ROSETTA-BREAST-01. This larger study is evaluating pumitamig plus chemotherapy versus placebo plus chemotherapy in patients with previously untreated locally advanced or metastatic triple-negative breast cancer who are ineligible for PD-(L)1 therapy because they have PD-L1 negative disease.

The partnership behind this drug represents a major bet from both companies. In June, BioNTech and Bristol Myers Squibb entered into a co-development and co-commercialization agreement worth $11 billion, focusing on BioNTech's investigational bispecific antibody BNT327 across numerous solid tumor types.

Price Action: BioNTech shares were down 0.94% at $96.37 at the time of publication on Tuesday. Bristol Myers Squibb shares were down 2.26% at $50.50.