Radiation hepatitis after postmastectomy radiation therapy for early breast cancer: difficult to differentiate from drug-induced liver injury caused by abemaciclib.

Abemaciclib (ABM) is recommended for adjuvant endocrine therapy in hormone receptor-positive, human epidermal growth factor receptor type 2-negative early breast cancer (EBC) patients at high risk of recurrence. Here, we present a case of radiation hepatitis challenging to differentiate from drug-induced liver injury during ABM treatment. The patient, a woman in her 40 s, underwent right mastectomy, axillary dissection, and postmastectomy radiation therapy (PMRT) after neoadjuvant chemotherapy for EBC. Subsequently, she received ABM as adjuvant endocrine therapy. Despite suspending ABM due to Grade 3 leukopenia, she developed Grade 3 hepatic dysfunction upon cessation. Based on the dynamic contrast-enhanced computed tomography, we diagnosed the cause of liver dysfunction as radiation hepatitis. Spontaneous improvement allowed us to resume ABM treatment. Clinicians may need to consider radiation hepatitis as a potential cause of hepatic dysfunction in patients who underwent PMRT, along with drug-induced liver injury.