# Primary large B-cell lymphoma of the patella with early systemic progression: A case report

## TL;DR

A rare case of primary large B-cell lymphoma in the patella rapidly spread despite treatment, highlighting diagnostic and therapeutic challenges.

## Contribution

This case report adds to the limited literature on patellar primary bone lymphoma and emphasizes the aggressive nature of non-GCB DLBCL subtypes.

## Key findings

- Primary diffuse large B-cell lymphoma of the patella is extremely rare with fewer than ten documented cases.
- The non-GCB subtype showed rapid systemic progression despite initial localized staging and R-CHOP treatment.
- Biopsy and immunohistochemistry are essential for diagnosing patellar PBL due to its similarity to metastases or other bone tumors.

## Abstract

Primary bone lymphoma (PBL) of the patella is an extremely rare condition, with fewer than ten documented cases. We herein described a unique case of primary diffuse large B-cell lymphoma (DLBCL) of the patella, highlighting its diagnostic challenges, therapeutic considerations, and unexpectedly rapid systemic progression, contributing valuable insights to the understanding of this uncommon entity.

A 68-year-old woman with a history of papillary thyroid carcinoma reported six months of worsening right knee pain, swelling, and reduced mobility. Imaging showed a lytic patellar lesion with cortical damage and soft tissue involvement. A biopsy confirmed non-germinal center B-cell-like DLBCL, identified by positive CD45, CD20, PAX5, MUM1, and BCL2 markers, and negative CD10, BCL6, and pan-cytokeratin results. PET/CT and bone marrow biopsy confirmed the disease was localized (stage IE). She received R-CHOP chemotherapy, but six months later, PET/CT revealed widespread progression to lymph nodes, adrenals, bones, breasts, and subcutaneous tissues. A breast biopsy matched the original DLBCL. Salvage chemotherapy with the R-ICE regimen (rituximab, ifosfamide, carboplatin, etoposide) was initiated. However, the patient’s clinical condition rapidly deteriorated, and she opted for palliative care.

Patellar PBL is challenging to diagnose due to its vague symptoms and similarity to metastases or other bone tumors, particularly in patients with prior cancer. Biopsy and immunohistochemistry were essential for confirmation. The rapid systemic spread, potentially tied to the non-GCB subtype, indicates an aggressive disease course, uncommon for early-stage PBL.

This case contributes to the sparse literature on patellar PBL, stressing the importance of biopsy for diagnosis and the need for close monitoring due to the risk of swift progression, even in localized disease. Further study of prognostic factors is warranted.

•Rare primary bone lymphoma in patella, <10 cases reported, non-GCB DLBCL enriches limited knowledge of this condition.•Early systemic progression under R-CHOP, aggressive non-GCB subtype suggests unpredictable behavior, challenges treatment.•Close follow-up critical; rapid progression needs research on prognostic factors, tailored strategies to improve outcomes.

Rare primary bone lymphoma in patella, <10 cases reported, non-GCB DLBCL enriches limited knowledge of this condition.

Early systemic progression under R-CHOP, aggressive non-GCB subtype suggests unpredictable behavior, challenges treatment.

Close follow-up critical; rapid progression needs research on prognostic factors, tailored strategies to improve outcomes.