# Rarity to Remission: Complete Response of Primary Breast Diffuse Large B‐Cell Lymphoma With Chemoimmunotherapy

## TL;DR

A rare case of primary breast lymphoma was correctly diagnosed and successfully treated with chemoimmunotherapy, achieving complete remission.

## Contribution

Demonstrates complete remission in a rare primary breast DLBCL case using R-CHOP chemoimmunotherapy.

## Key findings

- Primary breast DLBCL is rare and often misdiagnosed as carcinoma.
- R-CHOP chemoimmunotherapy achieved complete metabolic and pathological remission in this case.
- Immunohistochemistry is crucial for accurate diagnosis of primary breast lymphoma.

## Abstract

Primary Non‐Hodgkin's lymphoma of the breast is rare, accounting for < 0.5% of breast cancers and ~2% of extranodal lymphomas. It often presents as a painless lump, mimicking carcinoma and complicating diagnosis. Case PresentationWe report a 65‐year‐old post‐menopausal, hypertensive, and diabetic woman with a gradually enlarging left breast mass. Imaging revealed a suspicious lesion. Core biopsy suggested poorly differentiated carcinoma, but immunohistochemistry confirmed diffuse large B‐cell lymphoma (DLBCL), activated B‐cell subtype, with high Ki‐67 (~90%). PET/CT showed localized disease. She received six cycles of CHOP chemotherapy, with rituximab added from the second cycle. Treatment was well tolerated. Follow‐up PET/CT and biopsy demonstrated complete metabolic and pathological remission. ConclusionPrimary breast DLBCL is rare and easily misdiagnosed as carcinoma. Immunohistochemistry is therefore crucial for correct diagnosis. R‐CHOP chemoimmunotherapy is the cornerstone of treatment.

Primary breast lymphoma (PBL) is an uncommon extranodal lymphoma which often mimics carcinoma, leading to diagnostic delays. Immunohistochemistry is essential for accurate diagnosis. The optimal treatment modality is still under investigation because of the rarity of this disease. Chemoimmunotherapy with rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone (R‐CHOP) can achieve complete remission, highlighting its effectiveness in managing localized PBLs.

Baseline positron emission tomography/computed tomography (PET/CT) scan showing faintly FDG avid heterogenously enhancing soft tissue density lesion in the left breast (white arrow).