A New Era With Gedatolisib in Endocrine-Resistant Advanced Breast Cancer

Study Design and Arms

• Phase 3, randomized (1:1:1), open-label.
• Population: HR⁺/HER2⁻ advanced breast cancer (ABC) with progression after CDK4/6i; subgroup analyzed: PIK3CA-WT.
• Arms:
  1. Triple: Gedatolisib + Palbociclib + Fulvestrant
  2. Double: Gedatolisib + Fulvestrant
  3. Control: Fulvestrant
• Primary endpoint: PFS versus fulvestrant.
• Secondary endpoints: ORR, OS, safety, and quality-of-life measures.

Mechanism: Why Gedatolisib?

Gedatolisib, a dual-target PI3K/mTOR inhibitor (class I PI3K and mTORC1/2), targets resistance after endocrine therapy + CDK4/6i, in which the PI3K/AKT/mTOR pathway is often activated. Simultaneously suppressing two nodes may reduce adaptive escape compared with single-target inhibitors and provide synergy with fulvestrant .

Progression-Free Survival (PFS)—Months

HR: Triple 0.24, Double 0.33 (versus fulvestrant).

Dose & Safety (Study Protocol)

• Gedatolisib 180 mg IV weekly (Days 1, 8, 15) → 3 weeks on, 1 week off
• Palbociclib 125 mg PO → 21 days on / 7 days off
• Fulvestrant 500 mg (Days 1 and 15), then every 28 days 500 mg
• Discontinuation due to TRAEs: Triple 2.3%; Double 3.1%
• Hyperglycemia: Any-grade ~9.2–11.5%; Grade ≥3 ~2.3% (both geda arms)

Clinical note: Metabolic monitoring—fasting glucose and HbA1c—is recommended; the profile is consistent with the components and generally manageable.

DROZDOGAN Academy Commentary

VIKTORIA-1 results stand out after CDK4/6 inhibitors in HR⁺/HER2⁻, PIK3CA-WT advanced breast cancer as a long-awaited option that could fill a treatment gap.

• Clinically: Strengthening endocrine-based treatment offers an important second-line advance, especially for resistance after CDK4/6i without a PIK3CA mutation.
• Expected benefit: Substantially longer PFS—approximately 7 months—and dramatically higher responses represent major gains for patients at risk of early visceral progression.
• Clinical practice: Glycemic monitoring matters with diabetes or prediabetes. Overall, however, treatment was well tolerated and discontinuation was uncommon.
• Looking ahead: Maturing OS data and biomarker analyses will clarify which subgroups benefit most. For now, gedatolisib-based combinations have become strong second-line candidates.

🔹 In brief: These data strongly suggest moving beyond endocrine therapy alone after CDK4/6i.

Limitations

• OS data are not yet mature; final analysis is awaited.
• Open-label design; trial constraints on treatment selection may not reflect real-world practice exactly.

🧾 Conclusion & Message

VIKTORIA-1suggests that, after CDK4/6i, in PIK3CA-WT HR⁺/HER2⁻ advanced breast cancer, gedatolisib-based combinations could be strong 2nd-line options: mPFS 9.3 and 7.4 months; ORR 32% and 28.3%; manageable safety. Final OS and subgroup analyses will further clarify their role.