Immunoreactivity of Histiocytes to OCT4; a diagnostic pitfall

Abstract

Abstract Introduction/Objective Immunohistochemical stains are supposed to make a Pathologists’ life easier; however, interpretation of some stains in isolation can be a diagnostic pitfall. Immunoreactivity of paraganglia to OCT4 stain is a known pitfall for this stain when evaluating retroperitoneal lymph node dissection specimens for germ cell tumour metastasis. The purpose of this report is to highlight another pitfall of the OCT4 stain, albeit in a similar clinical scenario. Methods/Case Report A 49-year-old male with a history of left testicular seminoma metastatic to periaortic, retroperitoneal and left supraclavicular lymph nodes, status post orchiectomy and chemotherapy, presented with a rising B-HCG and PET scan evidence of recurrent/refractory disease. His imaging showed interval increase in FDG uptake of left periaortic lymph nodes despite a decrease in size. A biopsy was performed. Pathologic evaluation showed predominantly necrotic tissue with rare clusters of atypical cells with clear to pink cytoplasm, monotonous nuclei, and rare admixed lymphocytes. Immunohistochemical stains showed the atypical cells to be positive for OCT4 stain, raising the possibility of viable seminoma. However, additional satins showed the cells to be positive for CD68 and CD163, and negative for CD117, SALL-4, pancytokeratin, SF-1, GATA3 and synaptophysin. Therefore, the atypical cells were interpreted to represent histiocytes; no viable germ cell tumor was identified. Results (if a Case Study enter NA) NA Conclusion This case highlights the importance of using a panel of immunohistochemical stains, instead of relying on one stain, even if the stain is thought to be fairly specific. Pathologists need to be aware of immunoreactivity of histiocytes to OCT4 as a potential diagnostic pitfall in addition to the paraganglion cells staining for OCT4 being a pitfall.