AB049. Continuing challenges of primary neuroendocrine neoplasms of the thymus: clinicopathological characteristics of an uncommon tumor in a case series

Abstract

Background: Primary neuroendocrine neoplasms (PNEs) of the thymus are highly aggressive tumors that rarely occur. They account for 2–5% of all thymic neoplasms, and only 0.4% of all PNEs. Relatively few previously published studies have focused on neuro-endocrine tumors (TNEs). The aim of this study was to describe clinicopathological characteristics of this aggressive entity with literature review. Case Description: We report a retrospective study of 8 cases of PNEs of the thymus, diagnosed at our department of pathology and treated at our institution, with a hindsight of 20 years, from 2004 to 2024. The review of these 8 cases showed that there was no sex preponderance, with 4 male and 4 female patients, aged between 32 and 64 years, with a mean age of 49 years. The diagnosis was made on surgical resection (n=5) and transparietal biopsy (n=3). Intraoperative frozen sections were performed (n=7), showing a malignant tumor process (n=4), a non-small cell carcinoma (n=2) and malignancy that may be consistent with non-Hodgkin’s lymphoma or thymic carcinoma (n=1). The histological examination revealed tumors of only two subtypes and grades: intermediate grade carcinoid tumors (n=6) and high grade neuroendocrine carcinomas (n=2). The tumor cells shared similar immunohistochemical patterns, as all of the 8 cases were positive for synaptophysin and chromogranin, negative for muscle actin, PS100, CD5 and thyroid transcription factor-1 (TTF1). However, they are positive for CD56 (n=6), epithelial membrane antigen (EMA) (n=3) and pancytokeratin (n=1). Conclusions: Primary NEs of the thymus were observed to be an extremely aggressive but very rare malignant lesion. Their main differential diagnoses are extension or metastases of their bronchopulmonary counterparts. Early diagnosis and surgical resection are the most important methods to improve prognosis. In the future, multi-center, large-sample database and clinical studies are urgently needed to explore better treatment modality.