Lichenoid drug eruption induced by letrozole: a case report.

Lichenoid drug eruption (LDE) is an uncommon adverse reaction that can be clinically indistinguishable from idiopathic lichen planus (LP). We report a 63-year-old woman who developed a diffuse pruritic papular eruption with oral mucosal involvement two weeks after initiating letrozole for breast cancer. Histopathology revealed lichenoid interface dermatitis with scattered eosinophils extending into the deep subcutaneous tissue, supporting a drug-induced process. Due to the necessity of endocrine therapy, she was managed with high-potency topical corticosteroids and tacrolimus. Upon histologic confirmation, letrozole was replaced with exemestane, leading to a 90% improvement without recurrence. This case emphasizes the importance of clinicopathologic correlation and multidisciplinary coordination to maintain essential oncologic treatment while managing cutaneous toxicity.