PMC7803171_01
(a) CT right maxillary sinus mass. (b) Tumor cells forming sheets with a relatively cohesive growth pattern many exhibiting plasmablastic morphology (H&E, 400x). (c) Bizarre/anaplastic forms (H&E, 400x). (d) Abundant mitotic and apoptotic activity (H&E, 200x).
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Computed tomography (CT) revealed a 3.3 cm mass centered in the right maxillary sinus extending into the right nasal cavity, right retro maxillary space, and along the inferior extraconal compartment of the right orbit (Figure 1(a)). The patient underwent nasal endoscopy with bioptic material revealing effacement of architecture by a diffuse infiltrate composed primarily of large plasmablastic appearing cells with amphophilic cytoplasm, irregular nuclei, fine reticular chromatin, and occasional single, central nucleolus (Figures 1(b) and 1(c)). Brisk mitotic and apoptotic activity imparting a "starry sky" appearance and evidence of coagulative necrosis were noted (Figure 1(d)).
The large tumor cells are positive for MUM1 ((a) immunoperoxidase stain, 40x), partial positive for CD138 ((b) immunoperoxidase stain, 200x), and negative for CD20 ((c) immunoperoxidase stain, 40x) with Epstein-Barr virus-encoded RNA (EBER) transcripts identified by in situ hybridization ((d), 40x).
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Immunohistochemical profile (Figures 2(a) and 2(c)) was positive for CD138 (partial +) and MUM-1 (>30%), while negative for CD20. Epstein-Barr virus-encoded small RNA (EBER) was positive by in situ hybridization (ISH) (Figure 2(d)), c-MYC (>40%) had a strong and diffuse nuclear pattern of staining, and the proliferative rate by Ki-67 staining was high (>95%).
(a) Immunohistochemical stain for lambda, positive in the PBL (blue arrow) and predominately negative in the mature plasma cell component (red arrow) (100x). (b) Immunohistochemical stain for kappa, positive in the mature plasma cell component (red arrow) and essentially negative in the PBL cells (blue arrow) (100x). (c) Dual immunohistochemical stain for kappa and lambda showing lambda light chain restriction in the PBL cells (blue arrow) and kappa restriction in the mature plasma cell component (red arrow) (100x).
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Kappa/lambda staining by in situ and immunohistochemical methods (Figures 3(a) and 3(b)) revealed that the plasmablastic tumor cells exhibited lambda restriction. Ki-67 staining was low (<5%) (Figures 4(c) and 4(e)). Kappa/lambda staining by both in situ and immunohistochemical methods demonstrated the mature plasma cells exhibited kappa light chain restriction (Figures 3(a) and 3(b)). A dual stain of kappa/lambda by immunohistochemical methods clearly highlights the respective light chain restricted populations (Figure 3(c)).
(a) The mature plasma cell population (H&E, 200x). (b) Interface of PBL (blue arrow) and mature plasma cell population (red arrow) (H&E, 100x). (c)-(e) Interface of PBL and mature plasma cell population showing opposite expression of EBER-ISH ((c), 40x), Ki-67 ((d), 40x), and c-MYC ((e), 40x).
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A second distinct population of mature-appearing plasma cells without frank anaplastic/plasmablastic features was surrounding and contiguous to the PBL (Figures 4(a) and 4(b)). Ki-67 staining was low (<5%) (Figures 4(c) and 4(e)). Kappa/lambda staining by both in situ and immunohistochemical methods demonstrated the mature plasma cells exhibited kappa light chain restriction (Figures 3(a) and 3(b)).
Immunoglobulin heavy chain clonality testing by next-generation sequencing. (a) Results from the plasmablastic lymphoma demonstrating two distinct peaks consistent with a biallelic rearranged clone. (b) Results from the mature plasma cell neoplasm with inclusive results due to a low number of reads, but demonstrating an oligoclonal pattern with low-level detection of the biallelic clone found in the PBL population.
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The FR1 results of this testing are shown in Figures 5(a) and 5(b).
(a) Touch preparations from the PBL maxillary mass showing malignant cytology featuring enlarged nuclei, with high nuclear/cytoplasmic ratios, fine open reticular chromatin, and multiple prominent nucleoli (Diff-Quik stain, 1000x). (b) Aspirate smears from the bone marrow biopsy showing mature plasma cells (Wright-Giemsa, 1000x).
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Morphology revealed mature plasma cells without frank anaplastic/plasmablastic features (Figures 6(a) and 6(b)).