Breast malignant, males, children
Low grade myofibroblastic sarcoma

Author: Emily S. Reisenbichler, M.D. (see Authors page)

Revised: 20 September 2016, last major update September 2016

Copyright: (c) 2002-2016,, Inc.

PubMed Search: Low grade myofibroblastic sarcoma

Cite this page: Low grade myofibroblastic sarcoma. website. Accessed October 27th, 2016.
Definition / General
  • Spindle cell sarcoma with myofibroblastic differentiation
  • Also called myofibrosarcoma
Essential Features
  • Uncommon tumor overall, occurring predominantly in the head and neck or extremities with only rare reports within the breast
  • At least moderate cytologic atypia must be seen focally
  • Not part of WHO breast classification
Prognostic Factors
  • Frequently recurs, particularly when incompletely excised
  • Low rates of metastasis but lung is most common site when it occurs (Am J Surg Pathol 2001;25:219)
Case Reports
Gross Description
  • Well circumscribed tumor with firm, pale cut surface, despite infiltrative microscopic growth
Micro Description
  • Spindle cells in a fascicular or storiform growth pattern
  • Variable stromal collagen
  • Cells demonstrate pale eosinophilic cytoplasm and the nuclei must show at least moderate atypia focally and hyperchromasia
  • Diffusely infiltrative borders
Micro Images

Images hosted on PathOut servers:

Courtesy of Mark R. Wick, M.D.

Images hosted on other servers:

Low grade myofibroblastic sarcoma arising in fibroadenoma

Various images

Fig 1A: fascicular growth
Fig 1B: alpha smooth muscle actin+, vimentin+ (insert)
Fig 1C: fibronectin+ matrix
Fig 1D: type IV collagen negative

Positive Stains
Negative Stains
Electron Microscopy Description
  • Prominent rough endoplasmic reticulum, peripheral myofilaments and the fibronectin fibrils of the fibronexus junctions (J Clin Pathol 2009;62:236)
Electron Microscopy Images

Images hosted on other servers:

Ultrastructural features

Fig 2A: arrows point to thin filaments at the cell surface suggestive of fibronexus junctions
Fig 2B: arrows point to fibronectin fibrils extending into the extracellular matrix

Molecular / Cytogenetics Description
  • Gains at 1p11 → p36.3 (66%), 12p12.2 → p13.2 (45%), 5p13.2 → p15.3 (31%), +22 (28%), loss at 15q25 → q26.2 (24%) (Am J Clin Pathol 2009;131:701)
  • Complex DNA copy number changes
  • Higher average number of chromosomal aberrations than seen in nodular fasciitis
Differential Diagnosis
  • Desmoid fibromatosis: long sweeping fascicles with stromal collagen deposition; lacks cytologic atypia
  • Inflammatory myofibroblastic tumor: variably cellular fascicles; background lymphoplasmacytic infiltrate; lacks cytologic atypia; ALK positive in ~ 50%
  • Leiomyosarcoma: shorter fascicles, lacks stromal collagen, h-caldesmon positive
  • Myofibroblastoma: short, intersecting fascicles with stromal collagen deposition; lower mitotic activity; desmin and CD34 positive
  • Myofibromatosis: lacks cytologic atypia; biphasic fascicular and pericytoma-like areas; nodular growth, protruding into vascular spaces; lacks cytologic atypia
  • Nodular fasciitis: lacks fascicular growth pattern and cytologic atypia; border is typically not infiltrative; usually small (< 3 cm)
  • Solitary fibrous tumor: spindle cells lacking a fascicular architecture (i.e.“patternless pattern”); hemangiopericytoma-like vessels
  • Spindle cell (metaplastic) carcinoma: at least focal keratin positivity
  • Spindle cell rhabdomyosarcoma: fascicular growth; typically more cellular; positive myogenin and myoD1