Radiation Recall Myositis Associated with Abemaciclib—A Case Report—

Abstract

A 51-year-old woman who underwent right mastectomy and sentinel lymph node biopsy for right breast cancer was administered tamoxifen and a luteinizing hormone-releasing hormone (LH-RH) agonist as postoperative adjuvant therapy. Five years after surgery, a nodule measuring approximately 5 mm in size was resected from the right chest wall, confirming the recurrence of right breast cancer. Following radiation therapy, epirubicin + cyclophosphamide (EC) therapy was initiated but discontinued after two courses due to an allergic reaction. However, weekly Paclitaxel (PTX) was completed. Subsequently, the patient started receiving letrozole and abemaciclib. However, two months later, she experienced tightness in the right upper arm and stiffness in the right shoulder. The symptoms were consistent with the radiation field, and the imaging findings were consistent with the recall phenomenon caused by radiation therapy. Therefore, abemaciclib was considered the causative drug. Upon discontinuation of abemaciclib and initiation of rehabilitative therapy to restore shoulder mobility, the patient's right shoulder elevation, which had been previously limited to approximately 120°, rapidly improved. The patient has since continued letrozole and has since progressed without recurrence and without symptoms in the right upper limb. This case suggests that a recall phenomenon may occur following the administration of abemaciclib after radiation therapy.