Neuroendocrine marker expression in dendritic cell sarcoma.

Abstract

e23557 Background: Dendritic cell sarcoma (DCS) is a rare type of cancer that can involve lymph nodes (“follicular”) or occur outside of lymph nodes (“interdigitating”). These tumors are often challenging to diagnose on small biopsies. On a recent case at our institution, a biopsy of a left neck soft tissue mass showed a lesion with expression of neuroendocrine markers, which suggested the possibility of a primary neuroendocrine tumor. However, when the entire tumor was resected (left level 4 lymph node), it became clear that it was a 5.8 cm DCS, exposing this potential pitfall of interpretation of neuroendocrine markers in small biopsy cases. A literature search at the time (May 2024) revealed no significant academic studies characterizing the expression of neuroendocrine markers in these rare DCS tumors. Methods: IRB approval was granted and a search for in-house cases was conducted for a final diagnosis of “dendritic cell sarcoma” signed out between 8/27/2004 and 8/28/2024. A total of twelve archived in-house cases were identified in addition to the initial DCS case that inspired the search. All microscope slides and blocks for each case were acquired and reviewed. One block best representing the tumor was selected from each identified case. The selected blocks were stained with the Ventana immunohistochemical protocol for synaptophysin and chromogranin and the stained slides were reviewed. Results: Twelve cases with a diagnosis of dendritic cell sarcoma were identified. Of these twelve cases, five cases showed positive staining for synaptophysin. All twelve cases were negative for chromogranin. The sites of the cases positive for synaptophysin were lung (2), rectum (1), left upper quadrant soft tissue mass (1), and rib (1). The strength and distribution of positive staining was different for each case, with the strongest staining occurring in one lung case and rib, with the most sparse and weak positive staining occurring in the soft tissue mass. Conclusions: Dendritic cell sarcomas can variably express synaptophysin in varying proportions and levels. A potential pitfall exists when neuroendocrine expression in DCS possibly leads a pathologist to a different and potentially incomplete diagnosis. Interpretation of positive neuroendocrine expression including synaptophysin should not exclude DCS from the differential, especially on small biopsies where diagnosis of these tumors is difficult. Future studies are needed to determine the potential prognostic and predictive potential of neuroendocrine markers in DCS.