title: Low-grade myofibroblastic sarcoma arising in fibroadenoma of the breast-A case report.
abstract: BACKGROUND
  Myofibroblastic sarcoma or myofibrosarcoma is a malignant tumor of myofibroblasts and known to develop rarely in the breast, but its underlying lesion and tumor cell origin have never been reported yet.
  
  
  METHODS
  A 61-year-old female presented with a gradually growing breast mass with well-demarcated ovoid nodular shape. The tumor was histologically characterized by fascicular-growing spindle cell proliferation with large areas of hyalinized fibrosis and focally ductal epithelial remnants embedded in myxoid stroma, mimicking a fibroadenomatous lesion. It had frequent mitoses of 5-16/10 high-power fields, hemorrhagic necrosis, and focally pericapsular invasion. The spindle cells were diffusely immunoreactive for fibronectin, smooth muscle actin, and calponin, which suggest a myofibroblastic origin. Multiple irregularly thickened vessels with medial or pericytic cell proliferation were found to be merged with the intrinsic tumor cells. The tumor could be diagnosed low-grade myofibroblastic sarcoma arising in an old fibroadenoma.
  
  
  CONCLUSIONS
  We report a case of a low-grade mammary myofibrosarcoma that showed a background lesion of fibroadenoma first in the worldwide literature and suggest the pericytes or medial muscle cells of the intratumoral vessels as the cell origin of the myofibroblastic sarcoma.
authors.affiliation: Departments of Pathology, Dankook University College of Medicine, 119 Dandae-ro, Dongnam-gu, Cheonan-si, Chungnam, 31116, Korea. myongnh@dankook.ac.kr.
authors.forename: Na-Hye
authors.initials: NH
authors.lastname: Myong
authors.affiliation: Surgery, Dankook University College of Medicine, Cheonan, Korea.
authors.forename: Jun-Won
authors.initials: JW
authors.lastname: Min
mesh_terms: D014408:Biomarkers, Tumor / Q000032:analysis; D001706:Biopsy; D001943:Breast Neoplasms / Q000737:chemistry / Q000473:pathology* / Q000601:surgery; D049109:Cell Proliferation; D005260:Female; D018226:Fibroadenoma / Q000737:chemistry / Q000473:pathology* / Q000601:surgery; D006801:Humans; D007150:Immunohistochemistry; D008327:Mammography; D015412:Mastectomy, Segmental; D008875:Middle Aged; D008938:Mitosis; D058628:Myofibroblasts / Q000737:chemistry / Q000473:pathology*; D060787:Neoplasm Grading; D012509:Sarcoma / Q000737:chemistry / Q000473:pathology* / Q000601:surgery
chemical_list: D014408:Biomarkers, Tumor
keywords: Breast; Fibroadenoma; Myofibroblasts; Pericytes; Sarcoma