Fibroadenoma in axillary accessory breast tissue in a 22-year-old woman: a case report

Introduction and importance: Accessory breast tissue (polymastia) results from incomplete regression of the embryonic mammary ridge. It is most often found in the axilla and is subject to the same benign and malignant pathologies as normal breast tissue. Fibroadenoma arising in axillary accessory breast tissue is rare and may pose diagnostic challenges. Presentation of case: We report the case of a 22-year-old woman, mother of one child, who presented with progressive, painless, right axillary swelling that increased in size during pregnancy. Clinical examination revealed a well-defined, mobile, firm mass measuring approximately 2 × 2 cm. Ultrasonography revealed a well-circumscribed hypoechoic lesion suggestive of fibroadenoma. An ultrasound-guided true-cut core biopsy supported the diagnosis. After the mass was surgically removed, a histopathological analysis verified that a fibroadenoma had developed in accessory breast tissue. Clinical discussion: This case demonstrates how comprehensive clinical assessment, team-based diagnostic techniques, and patient-centered decision-making work together to provide the best possible results when managing breast pathology. Conclusion: This case highlights the importance of considering pathology arising from axillary accessory breast tissue when evaluating axillary masses, particularly in young women with hormonally responsive swelling.