Supplementary Material for: Apocrine adenoma of the breast showing unique image findings

Introduction: Apocrine adenoma of the breast is extremely rare and its typical images remain uncertain. Case presentation: A 66-year-old woman was incidentally found of her left breast tumor with computed tomography for ascending colon cancer staging work. Mammography showed a well-demarcated oval mass. Ultrasonography showed an oval mass with indistinct borders, internal iso-echoes with multiple high echo spots, and unchanged posterior echoes. Magnetic resonance imaging of the mass showed a hypo intense pattern both on T1- and T2-weighted images and a long-lasting rim enhancement pattern up to the late phase on time-signal intensity images. Probably due to the inappropriate tissue sampling, no definitive pathological diagnosis was obtained with core needle biopsy, forcing us to do lumpectomy of the breast mass at the time of colon cancer surgery. The resected breast mass was hard, clearly-demarcated, and 8mm in size. Cut surface of the mass was flesh-colored and had multiple white spots. Pathological study showed dense predominantly oval glandular ducts with luminal apocrine cell layers, outer myoepithelium cell layers, and slight fibrosis. Glandular cavities on pathology well matched to the white spots on macroscopic view, seemed vacant in a cyst-like fashion, and had aggregated foamy histiocytes in some of them. These pathological findings led us to the diagnosis of apocrine adenoma of the breast. Conclusion: Diagnostic physicians should note this extremely rare breast disorder and its image findings.