A Case of Liver Damage Caused by Abemaciclib Requiring Steroid Pulse Therapy

Background Cyclin-dependent kinase 4/6 inhibitors such as abemaciclib have become one of the first-line treatments for hormone receptor-positive, HER2-negative metastatic recurrent breast cancer. Although several side effects have been reported with the use of abemaciclib, Grade 4 drug-induced liver injury is rare. Case Presentation A 65-year-old woman presented for her initial visit. Magnetic resonance imaging revealed a tumor in her right breast. Biopsies of the breast and liver mass confirmed a diagnosis of T2N1M1 breast cancer in the upper outer quadrant of the right breast, hormone receptor-positive and HER2-negative. Treatment was initiated with letrozole and abemaciclib. On day 57 of treatment, Grade 3 liver enzyme elevation occurred, leading to a drug holiday. On day 127, a drug holiday was again required due to Grade 3 neutropenia, subsequently leading to a rise in alanine aminotransferase (ALT) to 1,396 U/L and total bilirubin (T-Bil) to 4.6 mg/dL, reaching Grade 4. Findings from serological tests and liver biopsy were consistent with drug-induced liver damage. By day 186, ALT began to decrease slightly, but with no downward trend in T-Bil, steroid pulse therapy was administered. The patient steadily improved and liver damage had nearly resolved by day 210. Exemestane alone was continued without recurrence of liver damage. Conclusion The incidence of Grade 4 liver damage due to abemaciclib is reported to be rare, ranging from 0 to 3%. Discontinuation of the drug due to adverse events carries the risk of worsening prognosis, making the management of these adverse events crucial.