Breast Mass as the Initial Presentation of B-Cell Acute Lymphoblastic Leukemia: A Case Report

Leukemic infiltration of the breast is an exceedingly rare clinical entity, often posing a significant diagnostic challenge as it can mimic common benign or malignant breast conditions. The presence of inflammatory features may further obscure the diagnosis, delaying appropriate intervention.

A 17-year-old female presented with a palpable right breast mass and axillary lymphadenopathy. Initial imaging revealed a 2.8 × 3.7 cm hypoechoic mass with indistinct margins and increased vascularity. Clinical findings were misinterpreted as an infectious or inflammatory process, particularly following excision of a reactive axillary lymph node. Her course was complicated by axillary vein thrombosis and a large pleural effusion. Subsequent clinical deterioration prompted a peripheral blood smear and bone marrow biopsy, which revealed B-cell acute lymphoblastic leukemia with 40% blasts, confirmed by immunohistochemistry (positive for LCA, CD20, PAX5, TdT). A breast biopsy performed after 1 month of chemotherapy revealed persistent extramedullary disease despite bone marrow remission. Treatment was escalated to hyper-CVAD, but the patient succumbed to complications, including neutropenic fever, pneumonia, and paraplegia.

This case underscores the diagnostic consequences of leukemic breast infiltration. A high index of suspicion for hematological malignancy is essential when evaluating breast masses, particularly in young patients with atypical features, unexplained systemic symptoms, or a progressive course despite antibiotics. Fine-needle aspiration (FNA) coupled with immunophenotyping or flow cytometry is a rapid and effective diagnostic tool that can prevent unnecessary surgeries and ensure the timely initiation of systemic chemotherapy for managing this aggressive disease.