# Extranodal marginal zone lymphoma presenting as a skin-based breast finding detected on screening mammography

## TL;DR

A rare case of skin-based breast lymphoma was detected through mammography and diagnosed with imaging and biopsy.

## Contribution

This case highlights the importance of imaging and biopsy in diagnosing rare skin-based lymphomas of the breast.

## Key findings

- A 72-year-old woman presented with a superficial breast mass detected on screening mammography.
- Ultrasound-guided biopsy confirmed low-grade B cell lymphoma with plasmacytic differentiation.
- PET/CT and biopsies confirmed disseminated stage IV extranodal marginal zone lymphoma.

## Abstract

Extranodal marginal zone lymphoma (EMZL) of the breast is rare and may mimic benign skin lesions at screening. We report a 72-year-old woman with a new superficial mass on screening mammography. Tangential views and ultrasound localized the abnormality to the dermis/subdermis, and ultrasound-guided biopsy revealed a low-grade B cell lymphoma with plasmacytic differentiation. Staging with PET/CT, a skin punch biopsy of a cutaneous shoulder lesion, and bone marrow biopsy confirmed disseminated disease, consistent with stage IV EMZL. This case underscores practical imaging steps, strategies, and differential diagnostic considerations to correctly identify skin-based findings and avoid misclassification. When appearances are new or atypical, particularly without a visible cutaneous correlate, tissue sampling is warranted to exclude malignancy, including dermal lymphoma.