Mediastinal seminoma: A case report with special emphasis on SALL4 as a new immunocytochemical marker

Abstract

Cytological diagnosis is a valuable method for detection of mediastinal tumors, and recent reports have shown the usefulness of fine-needle aspiration cytology for diagnosis of mediastinal tumors, including germ cell tumors. We report a case of mediastinal seminoma diagnosed intraoperatively by cytological examination of cystic fluid containing tumor cells. An anterior mediastinal tumor with cystic component was incidentally found in a 28-year-old Japanese male. Cytological examination of the cystic fluid at the time of tumor resection showed single and loose aggregates of large round to polygonal cells with large round nuclei, vesicular chromatin and nucleoli, and mild to moderate amounts of PAS-positive cytoplasm admixed with mature lymphocytes. A diagnosis of seminoma was made intraoperatively. On subsequent immunostaining, the tumor cells showed nuclear positivity for SALL4, a recently recognized germ cell marker that, in the appropriate setting, can be helpful to distinguish germ cell tumors from other mediastinal neoplasms, such as malignant lymphoma, thymoma, and thymic carcinoma.

SALL4, the missing link between stem cells, development and cancer

“…In solid tumors, SALL4 was first studied in germ cell tumors, where it is a sensitive diagnostic marker for primary central nerve system (CNS) germ cell tumors 66 , testicular germ cell tumors 67 , primary extragonadal germ cell tumors 101102 , mediastinal seminoma 103,104 , ovarian malignant germ cell tumor 105 , and metastatic germ cell tumors 106 . In yolk sac tumors and primary extragonadal germ cell tumors, one study reported that the circulating tumor cells are detectable by anti-SALL4 antibody in peripheral blood samples, making this protein a more sensitive marker than α-fetoprotein and glypican-3 107 .…”

The Utility of Fine Needle Aspiration (FNA) Biopsy in the Diagnosis of Mediastinal Lesions

“…A case of mediastinal seminoma misinterpreted as anaplastic thyroid carcinoma has also been reported [123]. Cell block preparations for immunohistochemical studies are helpful as seminomas will be positive for PLAP, CKIT, OCT3/4, SOX17, and SALL4 and negative for CD30 and AFP [119,[123][124][125]. Weissferdt and colleagues demonstrated that mediastinal seminomas can have CAM5.2 expression, albeit focally compared with thymomas and thymic carcinomas, which have diffuse staining.…”