PFE Stock Continues To Drop As Lung Cancer Trial Disappointment Overshadows Ibrance Win

The U.S. Food and Drug Administration approved the use of Ibrance as maintenance treatment for adults with a specific type of advanced or metastatic breast cancer on Wednesday.

• Investors continue to be weighed down by the mixed results from a late-stage lung cancer trial earlier this week. 
• Pfizer, on Monday, reported mixed topline results from a late-stage trial of sigvotatug vedotin, an antibody-drug conjugate it acquired through its purchase of Seagen in 2023.
• Stocktwits users highlighted disappointment over Pfizer’s acquisitions, including the recent purchase of obesity drugmaker Metsera.

Shares of Pfizer Inc (PFE) fell 3% on Wednesday in spite of the U.S. Food and Drug Administration approving a new use for its cancer drug Ibrance as investors continued to process the failed cancer trial data from earlier this week.

PFE shares have closed in the red for five consecutive days as of the end of Wednesday’s regular trading session.

The Fresh FDA Approval

The FDA approved the use of Ibrance as maintenance treatment for adults with a specific type of advanced or metastatic breast cancer on Wednesday.

Ibrance can now be given together with trastuzumab (with or without pertuzumab) and hormone therapy. It is approved for patients whose breast cancer is both hormone receptor-positive (HR+) and HER2-positive, after they have completed their initial round of treatment. This marks the first time a CDK4/6 inhibitor like Ibrance has been approved for patients with HR+ metastatic breast cancer regardless of HER2 status.

Strong Results From Key Study

The approval is based on results from the late-stage PATINA trial. In the study, adding Ibrance to standard anti-HER2 and hormone therapies reduced the risk of cancer progression or death by 24% compared with standard treatment alone. Patients who received Ibrance stayed free of disease progression for a median of 44 months, versus 29 months for those who did not receive it.

The safety profile of Ibrance in the trial was consistent with what doctors have already seen with the drug. The most common side effects were lower white blood cell counts.

About Ibrance

Ibrance has been a widely used treatment for HR-positive, HER2-negative metastatic breast cancer since its initial approval in 2015. It has been prescribed to more than 900,000 patients worldwide.

The new approval expands its reach to patients with HR+, HER2+ disease, a group that makes up about 10% of all breast cancers.

“Over the past decade, Ibrance has helped transform metastatic breast cancer treatment,” said Aamir Malik, Chief U.S. Commercial Officer and Executive Vice President at Pfizer. “With today’s FDA approval, Ibrance becomes the first and only CDK4/6 inhibitor indicated for patients with HR+ metastatic breast cancer regardless of HER2 status.”

Oncology Trial Result Disappointment Lingers

Pfizer on Monday reported mixed topline results from a late-stage trial of sigvotatug vedotin, an antibody-drug conjugate it acquired through its purchase of Seagen in 2023. In the late-stage study involving patients with previously treated advanced non-squamous non-small cell lung cancer, the drug failed to show a statistically significant improvement in overall survival compared to standard chemotherapy, docetaxel, in the overall patient population.

However, it showed encouraging trends toward better survival and progression-free survival in the subgroup of patients who had received only one prior line of therapy. Pfizer said the safety profile was manageable and plans to continue developing the drug, including in combination with immunotherapy in earlier treatment settings.

How Did PFE Retail Traders React?

On Stocktwits, retail sentiment around PFE stock stayed within the 'bullish' territory over the past 24 hours, while message volume stayed at 'high' levels.

A Stocktwits user opined that Pfizer must purchase smaller pharmaceutical company Sellas Life Sciences (SLS) to boost its cancer pipeline. Sellas has two main cancer drug candidates called Galinpepimut-S and SLS009.

Another user expressed disappointment over Pfizer’s purchase of Metsera last year. Pfizer bought obesity drugmaker Metsera in the second half of 2025 after a bidding war with Novo Nordisk for as much as $10 billion, after halting the development of its own obesity drugs.

PFE stock has fallen by about 5% year-to-date.

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