Breaking Resistance in Hormone-Positive Breast Cancer: Vepdegestrant Ushers In the PROTAC Era

Why Does It Matter?

Estrogen receptor-positive (ER+), HER2-negative advanced breast canceraccounts for approximately 70% of all breast cancers. Although standard first-line treatment includes combinations of endocrine therapy and CDK4/6 inhibitors , resistance commonly develops in advanced disease. One important cause of resistance is ESR1 mutations; after progression on a CDK4/6 inhibitor, these occur in 40-50% of patients.

However, treatment options for this group are limited and often challenging in clinical practice because of intravenous administration, weak efficacy, or substantial adverse effects. This is where the orally administered medicine with a new mechanism, vepdegestrant , enters the picture.

What Is Vepdegestrant, and What Does It Offer?

Vepdegestrant (ARV-471) is a PROTAC (proteolysis-targeting chimera)-based estrogen receptor degrader . This technology directs receptors to the ubiquitin–proteasome system for intracellular degradation. Unlike conventional ER antagonists, it not only blocks the receptor but also destroys it. This mechanism is particularly advantageous in suppressing mutant ER proteins.

What Did VERITAC-2 Investigate?

This multinational, open-label, randomized phase 3 study evaluated patients with advanced ER+/HER2– breast cancer who had previously received a line of CDK4/6 inhibitor plus endocrine treatment: 624 patients were included and assigned to two groups:

• Vepdegestrant: 200 mg orally each day

• Fulvestrant: Intramuscular injection twice a month

Randomization was based on ESR1 mutation status and the presence of visceral (internal organ) metastases .

The primary endpoint, measured by blinded central review, was radiographic progression-free survival (PFS) .

Important Success in Patients with ESR1 Mutations

In the ESR1-mutated subgroup, vepdegestrant was clearly superior:

• Median PFS:

  • Vepdegestrant: 5.0 months

  • Fulvestrant: 2.1 months

  • HR: 0.58 (confidence interval: 0.43–0.78), p<0.001

This represents a difference that is both statistically and clinically significant.

Moreover, in patients taking vepdegestrant, the objective response rate was 18.6% , compared with only 4.0% in the fulvestrant group.

Limited Benefit in the Overall Patient Population

In the overall population, including patients with and without ESR1 mutations, the difference was not significant:

• Median PFS:

  • Vepdegestrant: 3.8 months

  • Fulvestrant: 3.6 months

  • HR: 0.83, p=0.07

This finding may be associated with disease progression through multiple pathways and reduced sensitivity to endocrine therapy in patients without ESR1 mutations.

Adverse Effects and Safety

Treatment-related adverse effects were generally grade 1 or 2 . The most frequently reported were:

• Fatigue: 26.6% (vepdegestrant) vs. 15.6% (fulvestrant)

• Elevated liver enzymes (ALT, AST): 14.4%

• Nausea: 13.5%

Grade 3 or higher adverse events:

• Vepdegestrant: 23.4%

• Fulvestrant: 17.6%

QTc prolongation on ECG was rare, and no clinically significant arrhythmias were reported.

The rate of permanent discontinuation due to the medicine was low at just 2.9% .

Clinical and Scientific Commentary

📌 Compared with elacestrant and other oral SERDs, vepdegestrant offers a greater PFS gain in patients with ESR1 mutations.

📌 With a striking objective response rate of 18.6% , this new agent stands out as an important second-line alternative.

📌 Compared with fulvestrant, it offers advantages in both ease of administration (oral) and bioavailability.

Conclusion: Is the PROTAC Era Beginning?

VERITAC-2 demonstrated that, in patients with ESR1-mutated advanced breast cancer, vepdegestrant , compared with fulvestrant, provides longer progression-free survival and a higher response rate . The adverse effect profile is reasonable and generally manageable. Although overall survival (OS) data are not yet mature, this study may mark a milestone for PROTAC-based treatments entering clinical practice.