Case Report: Concurrent breast myeloid sarcoma and ductal carcinoma in situ—multimodality imaging findings and differential treatment response

Myeloid sarcoma (MS) is an uncommon extramedullary manifestation of myeloid neoplasms, and breast involvement is rare. We report concurrent breast MS and ductal carcinoma in situ (DCIS) in a 49-year-old woman who was referred for evaluation of cervical lymphadenopathy and subsequently underwent breast imaging for a rapidly enlarging palpable left breast mass. Mammography and ultrasonography showed a dominant noncalcified mass and separate calcification-associated lesions in the outer breast. Site-specific core biopsies identified MS in the noncalcified mass and concurrent MS and high-grade DCIS in a calcification-associated mass; an axillary lymph node also showed MS. Subsequent hematologic evaluation demonstrated BCR-ABL1-positive chronic myeloid leukemia (CML) with 3.5% bone marrow blasts, with extramedullary MS establishing blast-phase disease. MRI and FDG PET/CT performed after pathologic diagnosis demonstrated the extent of breast and extramammary disease. Approximately 5 weeks after initiation of systemic therapy, the enhancing breast lesions had markedly decreased on MRI. On follow-up ultrasonography, the mass component of the mixed MS and DCIS lesion also decreased, whereas the associated calcifications persisted. Mastectomy subsequently demonstrated residual DCIS without residual MS. Recognition of the different imaging patterns allowed separate sampling of morphologically distinct lesions and diagnosis of the two coexisting pathologic processes. Follow-up multimodality imaging demonstrated their different treatment responses.