A hidden diagnosis: Axillary ectopic breast cancer presenting as progressive lymphadenopathy: A rare case report and literature review

Ectopic breast cancer (EBC) is a rare malignancy arising from mammary tissue located outside the normal breast area, most commonly in the axilla. Its atypical presentation, often without associated breast abnormalities, can lead to delayed diagnosis. We describe the case of a 48-year-old woman presenting with progressive right axillary lymphadenopathy over 23 months. Imaging, including mammography and contrast-enhanced T1-weighted breast MRI, showed no identifiable primary breast lesion. Histopathological analysis of a core needle biopsy revealed undifferentiated carcinoma with positive hormonal receptor status, consistent with invasive lobular carcinoma arising from ectopic mammary tissue. The patient underwent neoadjuvant chemotherapy, surgical excision, axillary lymph node dissection, and received adjuvant radiotherapy and endocrine therapy. This case underscores the diagnostic challenge of EBC and highlights the importance of considering it in the differential diagnosis of axillary masses. Early histological confirmation and a multidisciplinary management approach are essential to optimize patient outcomes.