[Fibrin-associated large B-cell lymphoma confined to a left atrial myxoma showing durable remission after surgical resection alone].

Fibrin-associated large B-cell lymphoma is an extremely rare subtype of LBCL, characterized by distinctive pathological findings and symptoms, and is generally considered to follow an indolent clinical course. Here we report a case of fibrin-associated large B-cell lymphoma arising in association with an incidentally discovered left atrial myxoma, which has remained in remission with surgical resection alone. The patient was an 84-year-old woman. In September 2023, a routine preoperative chest X-ray performed prior to surgery for osteoarthritis of the shoulder revealed an abnormal shadow. Subsequent echocardiography demonstrated an intracardiac mass in the left atrium, and the patient was referred to our cardiology department. Echocardiography at our hospital revealed a pedunculated mass attached to the atrial septum, consistent with a diagnosis of left atrial myxoma. The mass measured approximately 80 mm and prolapsed between the left atrium and ventricle. Given the risk of obstruction, urgent surgical resection was performed. Histopathological examination of the resected specimen confirmed the diagnosis of fibrin-associated large B-cell lymphoma, and the patient was subsequently referred to the hematology department. A systemic workup revealed no evidence of additional disease. She has remained disease-free without any further therapy.