[1471] t(14;18)-Negative Interdigitating Dendritic Cell Sarcomas: A Morphologic and Immunohistochemical Review

RL Woodford, HY Wang, S Li, SE Mills, JB Cousar. University of Virginia, Charlottesville; UT Southwestern Medical Center at Dallas, Dallas; Emory University, Atlanta

Background: Interdigitating dendritic cell (IDC) sarcomas are exceedingly rare neoplasms that have not been fully characterized. Recent studies have reported rare IDC sarcomas harboring t(14;18) and/or clonal immunoglobulin heavy chain (IGH) gene rearrangements. In contrast, we have previously identified a group of IDC sarcomas that lack both of these molecular findings (manuscript submitted). These disparate results suggest significant molecular heterogeneity within IDC sarcomas. This study used histologic examination and immunohistochemistry (IHC) to evaluate three cases of t(14;18)-negative IDC sarcomas.
Design: Three cases of IDC sarcoma with adequate archival material were available for review. These cases were diagnosed according to the 2008 WHO criteria and were previously shown to be negative for t(14;18) and clonal IGH gene rearrangements. Patient age, sex, and tumor site were noted. Tumor morphology and other histologic features were assessed. IHC and in situ hybridization for EBV-Encoded RNA (ISH-EBER) were performed.
Results:

Clinical Features

CASE	AGE	SEX	SITE
1	35	M	Left lower quadrant of abdomen
2	73	F	Axillary lymph node
3	69	M	Parotid gland, level III lymph node

The tumors were composed predominantly of plump spindle cells, which were often arranged in fascicles. Variable whorling and storiform pattern were noted. Nuclei were vesicular with small to distinct nucleoli. The cytoplasm was eosinophilic with indistinct borders. Cytologic atypia ranged from mild (case 1) to marked (case 3). Mitotic activity demonstrated a similar spectrum (2/10 hpf in case 1, 16/10 hpf in case 3). Atypical mitotic figures were identified in cases 2 and 3. Admixed lymphocytes were predominantly T-cells, although plasma cells were also seen in two cases. Residual lymph node contained intact germinal centers. All tumors were immunoreactive for S100 and vimentin, while stains for CD21, CD35, D2-40, melanin A, HMB45, CD1a, Langerin, CD3, CD20, CD43, and CD45 were negative. Focal CD68 staining was occasionally seen. ISH-EBER was negative in all cases.
Conclusions: Although t(14;18)-negative IDC sarcomas demonstrate varied cytologic atypia and mitotic activity, their overall appearance and immunophenotype are consistent. Also, these tumors appear to be morphologically indistinguishable from those that harbor the t(14;18). Further study is needed to assess the clinical significance, if any, of the t(14;18) in IDC sarcomas.
Category: Hematopathology

Monday, March 22, 2010 9:30 AM

Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 198, Monday Morning