The radiographic appearance strongly favored colonic lymphoma.

Pathology report:
Abdominal biopsy: Fragments of granulation tissue infiltrated by an aggressive B-cell lymphoma showing a very high proliferative activity (about 100%).
On submitted immunostains the lymphoma cells are positive for CD45, CD20, CD79a, CD19,
CD10, BCL6, MUM1 (strongly and 100% of the cells) and cmyc (weakly and no more than 20-30% of the cells) and they are mostly negative for BCL2, CD23, CD21, CD30, CD15 and
cyclinD1. The CD3 and CD5 show a small number of reactive T lymphocytes and the Ki67
proliferation antigen is positive in about 100% of the cells. The AE1/AE3 cytokeratin is negative.

Conclusion:
This is an aggressive B-cell lymphoma.
The differential diagnosis is between Burkitt and diffuse large B-cell lymphoma.
Though part of the lymphoma cells in H&E stain seem to be of medium size, the morphological
features are technically suboptimal and not clear. Therefore no assessment can be made based on the morphology of the cells. However, according to the immunophenotypical results, the diagnosis of aggressive diffuse large B-cell lymphoma is favored. (strong and massive positivity for MUM1 and weak and scanty positivity for c-myc).

Primary colonic lymphoma is a rare entity, even more so in the pediatric-adolescent age group.