Thread by @SibaElHussein

Tricky case of Cyclin-D1-positive neoplasm➡️

Patient presented with "pancytopenia, rule out MDS"

Flow cytometry of a limited marrow aspirate revealed a CD20-positive Kappa restricted population that appeared to be negative for CD19 expression #hemepath #lymsm #mmsm #MedTwitter

Morphologic examination showed a hypercellular marrow almost completely involved by a "lymphoid" infiltrate with a low grade morphology

Although by flow cytometry, CD19 was negative, which is odd in a baseline presentation of a low grade lymphoma, CD20 stain was diffusely postive in the infiltrate (below)

Additional IHC workup targeting mantle cell lymphoma, follicular lymphoma, CLL/SLL, LPL/MZL was done

Cyclin D1 proved to be positive by IHC in a substantial subset of the infiltrate

However, CD5 was negative (by IHC & flow cytometry)

CD5 only highlighted background T-cells

Although CD5-negative mantle cell lymphomas exist, CD19-negativity was still bothersome

One other entity that can mimic this presentation is "Cyclin D1-rearranged plasma cell neoplam"

Cyclin D1-rearranged plasma cell neoplams can show B-cell marker expression (like CD20 & PAX5 etc), they also characteristically have a "lymphoid morphology" (the so called "small cell variant", more on this )shorturl.at/gnSY0

In addition plasma cell neoplasms in general may show many immunophenotypic aberrancies including loss of CD19 expression

Since this entity seemed to fit the bill more than a CD5-negative /CD19 negative mantle cell lymphoma, a myeloma tube was added by flow cytometry, and indeed showed an aberrant Kappa restricted plasma cell population, positive for CD20 & negative for CD19 expression

Below is an illustration of CD138 stain highlighting the neoplastic plasma cells

Cyclin D1 rearrangement was further detected by FISH

Take away messages➡️
🩸The small cell variant of plasma cell neoplasms is typically CCND1-rearranged & may mimic low grade B-cell lymphomas by morphology
🩸It can also show expression of B-cell markers that are typically not seen in myelomas

🩸Smoldering cases may present with pancytopenia only, mimicking MDS or low grade B-lymphomas
🩸Think of this entity when you are dealing with CCND1-positive neoplasm
🩸Other entities to think of when dealing with a CCND1-positive neoplasm is hairy cell leukemia

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