Roche breast cancer drug falls short of expectations (for now)

The Swiss pharma Roche must report a setback for its experimental oral breast cancer medicine named Giredestrant. The share price reacted with a notable dip. While earlier trials had produced encouraging results, the latest Phase III study fell short of its primary objective.

Giredestrant belongs to a new generation of so-called selective oestrogen receptor degraders (SERDs). These medicines are designed to block the oestrogen receptor in tumour cells and simultaneously trigger its breakdown. This slows the growth of breast cancer cells that depend on the hormone oestrogen. The approach is particularly relevant for ER-positive breast cancer, which accounts for around 70 per cent of all breast cancer cases.

Hope in the autumn

Only last year Roche had reported positive news. In the large Phase III lidERA trial, giredestrant demonstrated an advantage over the current standard endocrine therapy in patients with early-stage, hormone-dependent breast cancer. The drug reduced the risk of tumour recurrence more effectively than established treatment. For Roche this was an important success, as up to a third of patients with this form of cancer experience relapse despite therapy. The results also drew attention on the stock market: Roche shares rose significantly after the data were released.

Further support for the development came from another study, evERA, in which giredestrant showed positive results in patients with more advanced breast cancer in later treatment lines. On the basis of these data, the U.S. Food and Drug Administration has already accepted a New Drug Application for the therapy. Observers saw this as a sign that giredestrant could become an important addition to Roche’s oncology portfolio.

Disappointment in the spring

Expectations were therefore high for the results of the Phase III persevERA study. In this trial, giredestrant was tested in combination with the CDK4/6 inhibitor palbociclib as a first-line treatment for advanced or metastatic breast cancer. The combination was compared with the current standard therapy of letrozole plus palbociclib.

The outcome, however, proved less clear-cut than hoped. While treatment with giredestrant showed a numerical improvement in progression-free survival – the period during which the disease does not worsen – the difference was not statistically significant. The study therefore failed to meet its primary endpoint. On the positive side, the data confirmed that the therapy was well tolerated, with adverse events largely consistent with the known safety profiles of the individual medicines.

For Roche the result does not represent a complete failure, but it clearly tempers expectations. The company is therefore emphasising that the clinical development programme for giredestrant remains broad. Several large Phase III studies are still ongoing across different disease stages and treatment settings. Among them is the pionERA study, which is evaluating another combination therapy in endocrine-resistant breast cancer and is not expected to report results until 2027.

From hopeful contender to uncertain prospect?

Despite the latest disappointment, many analysts still see potential in the drug. Positive results in earlier stages of disease are considered particularly important, as large patient populations could ultimately be treated in that setting. Industry observers therefore continue to believe that giredestrant – if further trials prove successful – could become a key component of endocrine therapy for breast cancer.

Such an outcome would be strategically significant for Roche. Although the company already has a broad portfolio of cancer medicines, a new blockbuster from its internal pipeline could further boost growth in the coming years. Some analysts estimate potential long-term annual sales of around CHF 1.5 billion – though only if the drug continues to prove itself in clinical studies.

Even Roche chief executive Thomas Schinecker had previously highlighted giredestrant in annual press briefings as one of the most financially significant therapeutic candidates in the company’s pipeline. After the latest study results, however, the exclamation marks attached to that promise are now accompanied by a few question marks.