Abstract: FR-PO1235
Hyponatremia Associated with Cyclin-Dependent Kinase 4/6 Inhibitors CDK4/6i in Hormone Receptor-Positive, HER2-Negative Breast Cancer: A Case Series and Pharmacovigilance Review
Session Information
- Onconephrology: Diagnostic Dilemmas, Therapy-Related Toxicities, and Clinical Cases
October 23, 2026 | Location: Exhibit Hall A, Convention Center
Abstract Time: 10:00 AM - 12:00 PM
Category: Onconephrology
- 1600 Onconephrology
Authors
- Patel, Jaymin Bakul, University of Cincinnati, Cincinnati, Ohio, United States
- Warner, David M., University of Cincinnati, Cincinnati, Ohio, United States
- Sakhiya, Vipulbhai, Northwell Health, New York, New York, United States
- Jhaveri, Kenar D., Northwell Health, New York, New York, United States
- Gudsoorkar, Prakash Shashikant, University of Cincinnati, Cincinnati, Ohio, United States
Introduction
CDK4/6i (palbociclib, ribociclib, abemaciclib) is an FDA-approved therapy for hormone receptor-positive (HR+), HER2-negative (HER2−) metastatic breast cancer and some high-risk early-stage. Although electrolyte abnormalities are reported with these agents, clinically significant hyponatremia (HypoNa) and syndrome of inappropriate antidiuretic hormone secretion (SIADH) remain poorly characterized.
Case Description
We report 3 women with HR+/HER2− breast cancer status post radical mastectomy who developed hypoNa attributed to CDK4/6i. Clinical features, timing, management, and outcomes were reviewed, along with a focused FDA Adverse Event Reporting System (FAERS) analysis of hyponatremia reports in women receiving palbociclib, ribociclib, or abemaciclib. SIADH was diagnosed after alternative etiologies were ruled out. 2 were receiving abemaciclib and 1 ribociclib. Time to onset was 6–12 weeks after therapy initiation. Nadir serum sodium (SrNa) concentrations were 124, 126, and 128 mEq/L, respectively. All demonstrated improvement in SrNa with conservative therapy with temporary interruption of CDK4/6i. SrNa levels remained stable at 6-month follow-up.
Discussion
HypoNa from SIADH may represent an underrecognized adverse effect of CDK4/6i, particularly abemaciclib. Importantly, in our series, hypoNa responded to conservative interventions including fluid restriction, salt supplementation, and urea powder, allowing continuation CDK4/6i. Pharmacovigilance data further support a signal for hyponatremia across CDK4/6i. CDK4/6i-associated SIADH should be considered in breast cancer patients presenting with HypoNa. Early recognition and management may allow continuation of CDK4/6i therapy while maintaining SrNa stability; larger studies are needed to define incidence and mechanisms better.