Lichenoid dermatitis induced by abemaciclib in a patient with HR+/HER2- breast cancer.

Cyclin-dependent kinase (CDK) 4/6 inhibitors, such as palbociclib, ribociclib, and abemaciclib, are widely used in combination with endocrine therapy for the treatment of hormone receptor-positive (HR+) and human epidermal growth factor receptor 2-negative (HER2-) breast cancer. Despite their efficacy, these drugs are associated with a range of adverse events (AEs), including dermatologic toxicities. This case report presents a rare instance of lichenoid dermatitis in a 48-year-old woman following treatment with abemaciclib. The patient developed erythematous, edematous plaques and papules on her hands and forearms, which resolved after discontinuation of the drug and treatment with topical corticosteroids. This report highlights the need for awareness of cutaneous side effects associated with CDK4/6 inhibitors, particularly abemaciclib.