November 2020 — Hematopathology

The correct answer is mantle cell lymphoma, blastoid/pleomorphic variant (in the setting of lymphomatous polyposis of the colon).

The photomicrographs show portions of polypoid colonic mucosa and submucosa with a diffuse infiltrate of small- to intermediate-sized CD20-positive B-cells with irregular nuclear contours, blast-like chromatin, occastional prominent nucleoli, and scant cytoplasm which expand the lamina propria and distort the colonic architecture. Immunohistochemically, the neoplastic B-cells show aberrant expression of CD5, and nuclear overexpression of cyclin D1 and SOX11. The cyclin D1 overexpression is indicative of the traditional t(11;14) translocation involving CCND1 and IGH consistent with mantle cell lymphoma. The Ki-67 proliferation index, increased at 70%, fits with the increased mitotic rate seen on H&E and indicates a more aggressive neoplasm. Collectively, these features are diagnostic of an aggressive variant of mantle cell lymphoma, blastoid type.

Traditional mantle cell lymphoma can often be seen in the setting of lymphomatous polyposis of the colon in asymptomatic individuals and would show the same immunophenotype as our case. However this diagnosis is excluded based on the atypical blast-like/pleomorphic morphology.

Small lymphocytic lymphoma (SLL) is another CD5-positive B-cell neoplasm which rarely can involve the gut. However, SLL shows a specific immunophenotype and morphology which typically includes prominent pale proliferation centers and lack of cyclin D1 and SOX11 positivity.

While diffuse large B-cell lymphoma (DLBCL) can occasionally be positive for CD5, shows an increased Ki-67 proliferation index, and can involve the GI tract, the morphology, SOX11, and cyclin D1 positivity exclude this diagnosis. Using an endothelial cell nucleus or histiocyte nucleus as an internal “ruler,” we can see that the nuclei of the neoplastic B-cells are similar in size to these cells, which is helpful in excluding the large B-cells seen in DLBCL.

References
1. Swerdlow SH, Campo E, Harris NL, Jaffe ES, Pileri S, Stein H, Thiele JE (2017) WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues. Revised 4th edn. IARC, Lyon