Fibromastosis of the Breast

  • Fibromatosis (also called desmoid fibromatosis):
    • Is characterized by a proliferation of histologically bland spindle cells arranged in long fascicles, with infiltrative architecture:
      • Similar to fibromatosis in other sites
    • Fibromatosis is a rare tumor with:
      • Locally aggressive behavior
      • High incidence of local recurrence
    • Various causes have been accused of being its etiology including:
      • Genetic factors
      • Endocrine factors
      • Surgical trauma
    • For treatment of fibromatosis:
      • Wide local excision with adequate safety margins is considered the standard of care
  • The breast is an unusual site for occurrence of desmoid type fibromatosis with few cases reported in literature:
    • It represents 0.2% of all breast tumors
    • 4% of all extra-abdominal desmoid tumors
    • Bilaterality has been reported in:
      • 4% of cases
    • Most of these cases were reported in:
      • Young fertile females:
        • With rare cases reported in males
    • The reported risk factors include:
      • Surgical trauma
      • Silicone implants
      • Association with Gardener’s syndrome
    • Clinically, it is presented as a firm mass with skin dimpling and nipple retraction in superficial and retro-areolar tumors
      • Neither nipple discharge nor axillary lymphadenopathy commonly occur with fibromatosis 
    • Mammography:
      • Presents irregular walled and highly dense lesion with no calcifications mimicking sometimes breast carcinoma
    • Microscopic examination of desmoid tumor usually reveals:
      • The characteristic irregular bundles of spindle cells with regular nuclei surrounded by abundant collagen 
      • Giant cells, macrophages and lymphocytes:
        • Are noticed mostly peripherally 
    • Although fibromatosis does not have metastatic potential:
      • It can be locally aggressive
    • Metaplastic carcinoma (‘fibromatosis like,’ low-grade spindle cell):
      • Should be ruled out with keratin or other epithelial stains in every case
    • The differential diagnosis also includes:
      • Nodular fasciitis
      • Myofibroblastoma
      • Fascicular pseudoangiomatos stromal hyperplasia (PASH)
      • Stromal overgrowth of phyllodes tumors
      • Other spindle cell sarcomas
    • Fibromatosis may be very difficult to distinguish from scar / granulation tissue pathologically:
      • Especially in patients with prior resection and concern for recurrence
    • Beta-catenin nuclear staining:
      • Is characteristic of fibromatosis:
        • But is positive in only up to 70% of cases and may be difficult to demonstrate
Spindle cell proliferation formed of bland looking cell arranged in short fascicles with dissection of breast fat lobules at the periphery 
The cells showed diffuse positive nuclear staining for B-catenin 
  • References
  • Lee A, Gobbi H. Desmoid type fibromatosis In: Lakhani SR, Ellis IO, Schnit SJ, Tan PH, van de Vijver MJ et al. eds. WHO Classification of Tumours of the Breast. Lyon: IARC Press, 2012:131-2.
  • Schnitt SJ, Collins L. Biopsy Interpretation of the Breast. 3rd edition. Philadelphia, PA: Wolters Kluwer, 2018: 412-416.
  • Kuba MG, Lester SC, Giess CS, Bertagnolli MM3, Wieczorek TJ4, Brock JE. Fibromatosis of the breast: diagnostic accuracy of core needle biopsy. Am J Clin Pathol. 2017;148(3):243-250.
  • Kim T, Jung EA, Song JY, Roh JH, Choi JS, Kwon JE. Prevalence of the CTNNB1 mutation genotype in surgically resected fibromatosis of the breast. Histopathology. 2012;60(2):347-356.

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