# Unusual site, familiar pathology: A case of fibroadenoma in ectopic breast tissue

## TL;DR

A rare case of fibroadenoma in ectopic breast tissue in the axilla highlights the importance of considering this condition in axillary mass diagnoses.

## Contribution

This case report adds to the understanding of fibroadenoma occurrence in ectopic breast tissue and emphasizes its diagnostic implications.

## Key findings

- Fibroadenoma can occur in ectopic breast tissue in the axilla, a rare but important differential diagnosis.
- Imaging features like well-defined, oval, hypoechoic masses can help distinguish benign fibroadenomas from malignant lesions.
- Surgical excision of axillary fibroadenoma can be safely performed with good patient outcomes.

## Abstract

Fibroadenomas are among the most common benign breast tumors, typically occurring within the breast parenchyma. However, their occurrence in the axilla is rare and often originates from ectopic breast tissue (EBT), which develops due to incomplete regression of the embryologic mammary ridge. Although EBT is present in up to 6% of women, it is usually asymptomatic. When a mass is detected in the axilla, particularly in younger women, it often raises concern for lymphadenopathy or malignancy. This overlap in clinical presentation creates a diagnostic challenge. A 35-year-old woman presented with a 6-month history of a painless, palpable mass in the right axilla. Physical examination revealed a soft, mobile nodule. Mammography and ultrasound classified the lesion as BI-RADS-4A. An additional retro-areolar mass in the left breast showed similar BI-RADS-4A features. Core needle biopsies from both sites confirmed fibroadenomas. Due to patient preference, the axillary mass was surgically excised, and recovery was uneventful. This case illustrates a rare presentation of fibroadenoma arising in axillary EBT, underscoring the importance of considering ectopic breast tissue in the differential diagnosis of axillary masses. Careful imaging evaluation is essential to distinguish benign lesions, which often appear as well-defined, oval, hypoechoic masses, from suspicious features like irregular margins or increased vascularity that may suggest malignancy. Increased awareness of this entity can reduce diagnostic uncertainty, prevent unnecessary interventions, and guide appropriate patient-centered management.