Diagnose This (May 31, 2021)

This is a CD20 immunohistochemical stain. Knowing that these cells are mostly within peritubular capillaries, what is your diagnosis?

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This is an intravascular large B-cell lymphoma (LBCL), which is a rare type of LBCL that is characterized by the presence of neoplastic B cells limited to the lumen of small vessels. This is likely secondary to their lack of expression of surface proteins that allow transvascular migration. Malignant B cells are only rarely present in peripheral blood (5%) or bone marrow.  The patient also had pituitary enlargement, adrenal insufficiency, and anemia, for which a bone marrow biopsy was performed with negative results. The diagnosis was established through a renal biopsy performed due to elevated serum creatinine. Urine sediment was unremarkable.

https://www.sciencedirect.com/science/article/pii/S0006497120606875