Breast
Other benign tumors
Myofibroblastoma


Minor changes: 30 June 2020

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PubMed search: Myofibroblastoma [title] breast [title]

Samaneh A. Motanagh, M.D.
Kristen E. Muller, D.O.
Page views in 2019: 9,659
Page views in 2020 to date: 6,290
Cite this page: Motanagh SA, Muller KE. Myofibroblastoma. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/breastmyofibroblastoma.html. Accessed July 8th, 2020.
Definition / general
  • Benign spindle cell tumor of mammary stroma composed of fibroblasts and myofibroblasts with recurrent monoallelic loss of 13q14 region including RB1
  • First recognized in 1981 and described by Wagotz in 1987 (Am J Surg Pathol 1987;11:493)
Essential features
  • Well circumscribed spindle cell tumor comprised of short fascicles of bland spindled cells and dense hyalinized collagen bundles
  • Variants include collagenized / fibrous, cellular, infiltrative, myxoid, deciduoid, epithelioid, lipomatous and atypical
  • Part of 13q / Rb family of tumors as majority show deletion or rearrangement of 13q (13q14) which may result in loss of Rb expression by immunohistochemistry
  • Benign and adequately treated by excision alone
Terminology
  • Benign stromal spindle cell tumor with predominant myofibroblastic differentiation
ICD coding
  • ICD-O: 8825/0 - myofibroblastoma
  • ICD-10: D24.9 - benign neoplasm of unspecified breast
  • ICD-11:
    • XH8JB0 - myofibroblastoma, mammary type
    • XH3NQ0 - myofibroblastoma
    • 2F30 - benign neoplasm of breast
Epidemiology
Sites
Pathophysiology
Etiology
Clinical features
  • Painless, nontender, slow growing, mobile mass
  • Clinically mistaken for fibroadenoma
Diagnosis
  • Imaging: ultrasound, mammogram, MRI
  • Invasive procedure: biopsy, fine needle aspiration (FNA)
Radiology description
Radiology images

Contributed by Kristen E. Muller, D.O.

Ultrasound, well circumscribed mass

Ultrasound, multilobulated mass

Mammogram

Mammogram, multiple masses

Prognostic factors
  • Clinically benign behavior, local excision is curative
  • No tendency for recurrence or distant metastasis (Virchows Arch 2002;440:249)
Case reports
Treatment
  • Surgical excision alone
Clinical images

Images hosted on other servers:

Myofibroblastoma in gynecomastia

15 cm tumor

Gross description
Gross images

Images hosted on other servers

13 cm, lobulated
white cut surface

Microscopic (histologic) description
  • Well circumscribed, lacks true capsule, rarely infiltrative
  • Bland, uniform, short to elongated spindle cells arranged as short haphazard intersecting fascicles admixed with bands of hyalinized, brightly eosinophilic collagen and variable amounts of fat
  • No more than mild nuclear atypia
  • Mitoses usually absent, atypical mitoses and necrosis absent
  • Mast cells common, perivascular lymphocytic infiltrates on occasion
  • Focal myxoid stromal changes common
  • May show smooth muscle leiomyomatous differentiation (elongated spindle cells with cigar shaped nuclei and pink cytoplasm)
  • Rarely cartilaginous or osseous components
  • Variants:
    • Collagenized / fibrous: collagenous stroma predominates, may have hypocellular myofibroblastic spindle cell component
    • Cellular: dense proliferation of myofibroblasts, ratio of spindle cells to collagen increased compared to classical variant, may have infiltrative borders, storiform or herringbone arrangement
    • Infiltrative: irregular margins, grows into surrounding mammary parenchyma entrapping glandular tissue
    • Myxoid: stellate and spindle cells in abundant myxoid stroma (Histol Histopathol 2016;31:1)
    • Deciduoid: large round, polygonal cells with abundant eosinophilic glassy cytoplasm, single or multiple prominent nucleoli which may be eccentrically placed, binucleation, sharp cell borders, eosinophilic intracytoplasmic inclusions (Histopathology 2008;52:652)
    • Lipomatous: abundant adipocytic component
    • Epithelioid: oval to polygonal cells arranged in clusters, cords, alveolar groups, linear strands, mono, bi or multinucleated, may have eccentrically placed nuclei with small nucleoli, well defined cell borders, single file arrangement may mimic invasive lobular carcinoma (Am J Surg Pathol 2009;33:1085)
    • Atypical: single or scattered atypical mono or multinucleated cells with mild to severe nuclear pleomorphism, regarded as degenerative (Arch Pathol Lab Med 2008;132:1813)
Microscopic (histologic) images

Contributed by Kristen E. Muller, D.O.
Well circumscribed mass

Well circumscribed mass

Classical type

Classical type

Hypocellular, collagenized / fibrous variant

Hypocellular, collagenized / fibrous variant

Collagenized / fibrous variant

Collagenized / fibrous variant

Admixed adipocytes

Admixed adipocytes

Lipomatous variant

Lipomatous variant


Myxoid stroma

Myxoid stroma

Myxoid stroma and fat

Myxoid stroma and fat

Mast cells

Mast cells

Cellular variant

Cellular variant

Epithelioid variant

Epithelioid variant

Epithelioid / deciduoid variant

Epithelioid / deciduoid variant


Epithelioid with single file growth

Epithelioid with single file growth

Smooth muscle differentiation

Smooth muscle differentiation

Chondroid metaplasia Chondroid metaplasia

Chondroid metaplasia

Focal cytological atypia

Focal cytological atypia

Lipomatous variant

Lipomatous variant


Lipomatous variant

Lipomatous variant

CD34

CD34

Desmin

Desmin

ER

ER

PR

PR

Loss Rb1

Loss Rb1

Virtual slides

Images hosted on other servers:

Breast, myofibroblastoma

Cytology description
Cytology images

Images hosted on other servers

Loosely cohesive myoepithelial cell groups

Positive stains
Negative stains
Electron microscopy description
Molecular / cytogenetics description
Sample pathology report
  • Left breast, mass, needle core biopsy:
    • Bland spindle cell lesion consistent with myofibroblastoma (see comment)
    • Comment: Sections show bland spindle cells arranged in short fascicles admixed with hyalinized collagen bundles and adipose tissue. The lesional cells express CD34, desmin, smooth muscle actin, BCL2 and PR, are negative for cytokeratins and show a loss of Rb1 by immunohistochemistry. Overall, the morphologic and immunohistochemical findings are compatible with mammary type myofibroblastoma.
Differential diagnosis
Board review style question #1

Which of the following immunohistochemical stains is positive in the lesion depicted above?

  1. AE1 / AE3
  2. Calponin
  3. CD34
  4. p63
  5. S100
Board review answer #1
C. CD34. The image shows a myofibroblastoma.

Comment Here

Reference: Myofibroblastoma
Board review style question #2
Which of the following is true regarding mammary type myofibroblastomas?

  1. The cellular and epithelioid variants are positive for cytokeratins
  2. They are always CD34 positive
  3. They are genetically related to spindle cell lipoma and cellular angiofibroma and cytogenetically show monoallelic loss of 13q14 region
  4. They are related to solitary fibrous tumors and are STAT6 positive by immunohistochemistry
  5. They may have aggressive behavior if cytologic atypia is present
Board review answer #2
C. They are genetically related to spindle cell lipoma and cellular angiofibroma and cytogenetically show monoallelic loss of 13q14 region

Comment Here

Reference: Myofibroblastoma
Board review style question #3
Which immunoprofile is most suggestive of mammary type myofibroblastoma?

  1. CD34 negative, desmin positive, smooth muscle actin positive, Rb1 positive
  2. CD34 negative, desmin negative, cytokeratin positive, Rb1 negative
  3. CD34 positive, desmin positive, CD10 negative, Rb1 positive
  4. CD34 positive, desmin positive, STAT6 negative, Rb1 negative
  5. CD34 positive, STAT6 positive, Rb1 positive
Board review answer #3
D. CD34 positive, desmin positive, STAT6 negative, Rb1 negative

Comment Here

Reference: Myofibroblastoma
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