#00064956

A 36-year-old female with a history of B-cell acute lymphoblastic lymphoma/leukemia (B-ALL) status post-chemotherapy with persistent minimal residual disease in the cerebrospinal fluid presented for restaging. PET/CT showed a fluorodeoxyglucose avid breast mass. The breast mass was biopsied. (A) Hematoxylin and eosin stain (40X) of the breast mass biopsy showed an infiltrate of medium to large blasts with fine chromatin, some with distinct nucleoli and scant cytoplasm. Immunohistochemistry (all at 40X) demonstrated that the blasts were (B) strongly positive for terminal deoxynucleotidyl transferase (TdT), (C) positive for PAX-5, (D) weakly positive for CD19, (E) strongly positive for CD10 and (F) negative for CD34, supporting an immature B phenotype. The histopathologic findings, with the patient’s clinical history is consistent with a relapse of B-ALL.  Extra-medullary relapse of B-ALL can be seen, but very rarely observed in breast as a distinct mass lesion.