AB043. One case report of recurrence of atypical A thymoma subsequent to undergoing surgery for type AB thymoma

Background: The atypical type A thymoma is a newly recognized entity in the latest histologic classification by the World Health Organization (WHO) [2015], characterized by an uncertain prognosis.

Case Description: Here, we present a case of a 54-year-old male patient who underwent thoracoscopic resection of a mediastinal tumor and partial thymic tissue under the left thoracic approach in 2013. At that time, chest computed tomography (CT) revealed a left anterior superior mediastinal tumor during examination at another hospital. Postoperatively, the pathology confirmed AB type thymoma with incomplete envelope and tumor-node-metastasis (TNM) stage T1bN0M0. After 3 years of follow-up, the patient’s condition stabilized without further intervention. In 2020 (7 years after surgery), the patient presented to Affiliated Hospital of Qingdao University with swelling and pain in the chest wall. Physical examination revealed a hemispherical mass on the left chest wall, while positron emission tomography/CT (PET/CT) showed two soft tissue density nodules [standardized uptake value (SUV) 2.8] within the previously operated area of the left anterior superior mediastinum. Additionally, there was involvement of the entire chest wall and ribs by the mass on imaging findings. After excluding surgical contraindications, we performed an open surgery via the left sixth intercostal rhomboid incision approach in June 2020. During the procedure, we resected portions of the left fifth, sixth, and seventh ribs and excised both the left mediastinal mass and chest wall mass. Subsequently, titanium mesh was utilized to reconstruct the bony chest wall, while a latissimus dorsi myocutaneous flap was employed to repair the skin defect. The postoperative pathology revealed an atypical type A thymoma with metastasis to the chest wall. After the operation, the patient underwent local radiotherapy to the chest. During radiotherapy, the patient exhibited symptoms of myasthenia gravis, such as generalized weakness and difficulty in mastication, which gradually deteriorated. Subsequently, the patient was prescribed 60 mg of oral pyridostigmine bromide bid in combination with immunoglobulin shock therapy. The patient gradually recuperated and continued to complete all postoperative radiotherapy. After 4 years of follow-up, the patient’s condition was stable, and he resumed normal work and life.

Conclusions: Atypical type A thymoma represents a collection of various subtypes within the atypical type A category. Its clinical significance remains to be established, necessitating further investigation and comprehensive clinicopathological data. Ongoing follow-up studies are being conducted to facilitate additional research in this area.

Keywords: Thymoma; atypical type A thymoma; case report