Primary mucinous adenocarcinoma of the thymus; a rare type of thymic carcinoma. Case Report.

Mucinous adenocarcinoma of the thymus is a particularly rare type among thymic carcinomas. Here, we report a patient who underwent complete surgical resection of the primary mucinous adenocarcinoma of the thymus. She was 74 years old and presented with a 60-mm multilocular cystic tumor in her right anterior mediastinum. We performed extended thymo-thymectomy with partial resection of the right upper lobe and pathologically diagnosed the patient with Masaoka stage II mucinous adenocarcinoma of the thymus. Immunohistochemistry showed the absence of PD-L1, suggesting that immune check point inhibitors targeting PD-1/PD-L1 might not be effective in this case. The increased preoperative serum levels of CA19-9 decreased after the operation. CA19-9 is a biomarker for disease status. Future reports should help elucidate the pathogenesis of this disease.