Challenges of Renal Function Assessment in Breast Cancer Patients Treated With Abemaciclib: A Case Report.

Abemaciclib, a cyclin-dependent kinase 4/6 (CDK4/6) inhibitor used for hormone-receptor-positive and human epidermal growth factor receptor 2 (HER-2)-negative breast cancer, can lead to elevated serum creatinine without implications on the true renal function. Although clinical trials have shown no increase in other kidney function biomarkers, this may still represent a challenge in cancer patients. We report a case of a 74-year-old female who presented with creatinine and cystatin-C elevation during treatment with abemaciclib without an equivalent decrease in measured glomerular filtration rate (GFR) with renal scintigraphy. The confirmation of adequate kidney function allowed for the maintenance of treatments that would otherwise be limited by renal impairment. Healthcare providers should be aware of abemaciclib's effect on serum creatinine but should not eliminate the possibility of actual kidney injury. Alternative biomarkers for GFR assessment are recommended, although the usefulness of cystatin-C in patients receiving abemaciclib should be investigated in greater depth.