Liver toxicity with ribociclib in a patient with metastatic hormone receptor positive postmenopausal breast cancer.

Liver adverse reaction occurred due to ribociclib use in the patient who had no history of any other disease. The Naranjo algorithm score was evaluated as 9. Considering the excretion of ribociclib by sulfation, cysteine conjugation, and glucuronidation, which are phase II reactions, n-acetyl cysteine (NAC) treatment (600 mg/day) was started for the patient. NAC therapy is recommended to reduce elevated liver enzymes in the case. The patient's treatment has been continuing with palbociclib for 5 months. No increase in liver enzymes was observed.