Relapsing eosinophilic pneumonia in a patient with recurrent breast cancer receiving abemaciclib plus endocrine therapy.

This report presents the case of a 42-year-old Japanese woman with recurrent hormone receptor-positive breast cancer who developed eosinophilic pneumonia (EP) during treatment with abemaciclib combined with endocrine therapy. Seven years after a radical surgery and definite diagnosis of Stage I breast cancer, her cancer recurred with metastases to multiple organs. Initially treated with abemaciclib plus letrozole and goserelin for 3 months, she developed EP, which improved after the discontinuation of anti-cancer treatment and the administration of prednisolone. However, EP occurred again upon the reintroduction of endocrine therapy (i.e., letrozole and goserelin). It improved gradually with the suspension of endocrine therapy and the re-administration of prednisolone. This case underscores the need for further research into the prevention and management of EP in patients receiving abemaciclib with endocrine therapy for advanced breast cancer.