Microscopy: Both cores consist of a partly necrotic malignant tumor comprising sheets of large atypical lymphoid cells. The tumor cells have scant cytoplasm, moderately pleomorphic nuclei with vesicular chromatin. Apoptotic bodies are frequent. No well-formed follicles are evident. No Reed-Sternberg cells are seen. A focal intra tumoral infiltrate of histiocytes is present.
Immunoperoxidase stains have been performed and the tumor cells have the following immune profile:
Positive: CD10, CD20, MUM1 (30%), Bcl6, c-myc (50%).
Negative: CD3, CD5, Bcl2, CD30, cyclinD1, TdT.
Ki-67 shows a proliferative index of approximately 75%.

Conclusion: Mesenteric mass, core biopsy: High-grade B cell lymphoma. FISH will be requested in an attempt to distinguish double hit high-grade B cell lymphoma from diffuse large B-cell lymphoma.