Non-mucinous, enteric-type thymic adenocarcinoma: genetic analysis of a case

Thymic adenocarcinoma is a rare histological subtype of thymic carcinoma. Non-mucinous enteric-type thymic adenocarcinomas are extremely rare.

A 54-year-old woman with an abnormality detected on chest radiography was admitted to our hospital. Chest computed tomography showed a 5.5-cm-diameter mass in the anterior mediastinum. Blood carcinoembryonic antigen (CEA) level was highly elevated at 127 ng/ml (normal < 5), while other tumor markers, including alpha-fetoprotein, β-human chorionic gonadotropin, and interleukin-2R levels, were normal. Radiological findings suggested that the tumor was a thymic epithelium (Masaoka stage III). Surgery is performed for diagnostic and therapeutic purposes. Intraoperative findings revealed extensive pericardial invasion requiring a median sternotomy. The left brachiocephalic vein, pericardium, and lungs were resected along with the tumor to achieve complete resection. Histological findings revealed that the tumor was composed of tall, columnar adenocarcinoma forming irregular lumina with no mucin production. Immunohistochemistry showed that cytokeratin 20 was partially positive and caudal type homeobox 2 was positive in approximately 50% of the tumor cells. Based on the morphological and immunohistochemical findings, enteric-type thymic adenocarcinoma was diagnosed per the 5th edition of the World Health Organization classification. The tumor was subtyped according to the Masaoka (stage IVB) and TNM classification criteria (T3N1M0 stage IVA). Plasma CEA levels decreased to normal levels after surgery. Further genetic analysis of the tumor revealed a pathogenic TP53 stop-gain mutation (p.Arg213*), leading to the loss of p53 protein function. Postoperative adjuvant radiation therapy (54 Gy in 27 fractions) was administered under the suspicion of incomplete microscopic resection. Reportedly, the patient is in complete remission four years post-surgery.

We encountered a rare case of non-mucinous enteric-type thymic adenocarcinoma harboring a pathogenic TP53 mutation. Further studies are required to enunciate the features of this subtype of thymic carcinoma.