AB035. PS01.17: Primary thymic adenocarcinoma with signet ring cell features to a 39-year-old male: a case report

Abstract: We describe a case of primary thymic adenocarcinoma, an extremely uncommon neoplasm with only 43 cases reported in literature. Patient was a 39-year-old male who presented with an anterior mediastinal mass extending to the left supraclavicular area. He later developed bilateral pleural and pericardial effusions which led to his untimely demise. A small biopsy from the left supraclavicular area was done post-mortem which showed back to back arrangement of neoplastic glands and occasional signet-ring cells. The initial diagnosis was metastatic adenocarcinoma with signet-ring cell features, but extensive clinicoradiologic work-up failed to reveal a primary tumor elsewhere. Immunohistochemically, the tumor cells were reactive for CK-7, CEA, and CD5 and non-reactive for CK-20, TTF-1, NAPSIN A, AFP, PAX-8, CD-117, CA19-9, CA-125, CDX2, P63, CD45 and CD99. The morphologic and immunophenotypic similarities of thymic adenocarcinomas with signet ring cell features from the lungs, stomach, and pancreas can pose diagnostic challenges for surgical pathologists especially for small biopsy specimens where origin from a dysplastic thymic epithelium or a thymic cyst cannot be ascertained. Therefore, a thorough clinical and radiological work-up with immunohistochemical investigation is critical. The findings in this case further broaden the morphologic spectrum of thymic adenocarcinomas.

Keywords: Thymus gland; adenocarcinoma; signet ring cells