[650] Inflammatory Reactions in Mesotheliomas: Diagnostic Pitfalls of Lymphohistiocytic Pattern, Lymphoid Reaction Mimicking Lymph Node Metastasis, and Fibrosclerosing Pattern Mimicking Sclerosing Mesenteritis

Thomas Huebner, Jennifer A Collins, Allen Burke. UMMC, Baltimore, MD

Background: Diffuse malignant peritoneal mesothelioma (DMPM) may be associated with a brisk inflammatory reaction. The histologic features of these tumors have not been studied.
Design: We retrospectively reviewed the histologic features of 66 DMPM to assess pitfalls in diagnosis associated with marked inflammatory reaction. In each case, debulking with multiple resection sites was performed prior to hyperthermic intraperitoneal chemotherapy treatment. Immunohistochemical studies were performed.
Results: Of 66 DMPM, there were 16 with a marked inflammatory reaction (24%)(9 women, 51 ± 11, 7 men, 61 ± 6 years). The inflammatory response comprised three patterns: nodular lymphoid hyperplasia with germinal centers (n=11); a lymphohistiocytic response (n=3) and a sclerosing mesenterits-like pattern with broad fibrous bands and lymphoid aggregates (n=2). 3 patients had prior chemotherapy with pemetrexed and cisplatin; these tumors all had nodular lymphoid hyperplasia. 4/50 patients without inflammatory reaction had prior systemic chemotherapy (p=0.3). 4 tumors were epithelioid tubulo-papillary, 12 epithelioid with solid growth, and 2 biphasic with spindled areas. The inflammatory DMPM were more likely to have deciduoid areas (n= 9) as compared to DPMP without inflammation (p=.01). Of the11 tumors with nodular lymphoid hyperplasia, 4 had mesenteric nodules with a lymphoid reaction around them mimicking lymph node metastasis. None of the 66 tumors demonstrated true lymph node metastasis. 3 tumors had areas of lymphohistiocytic growth pattern, with plasmacytoid malignant cells; in two of these cases there was readily identified tubulo-papillay and epithelioid deciduoid features. In those tumors with a sclerosing mesenteritis-like pattern, there were large areas devoid of malignant cells in one case. Immunohistochemical staining demonstrated diffuse positivity for calretinin in 15/16, EGFR in 15/16, and D2-40 in 9/16. One tumor with a lymphoplasmacytic pattern was negative for all mesothelial markers as well as markers of serous papillary differentation.
Conclusions: A prominent lymphoid reaction is present in about 1 in 4 peritoneal mesotheliomas. The lymphoid hyperplasia may mimic lymph node metastasis. A lymphochistiocytic pattern can mimic an inflammatory or lymphoproliferative process, but typical epithelioid areas are usually present. A sclerosing mesenteric-like pattern can obscure the malignant process, but this pattern is the most unusual.
Category: Gastrointestinal

Wednesday, March 6, 2013 9:30 AM

Poster Session V # 114, Wednesday Morning


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