Nodular Fasciitis
(Infiltrative or Pseudosarcomatous Fasciitis)
Epidemiology:
- Young adults often
- All age groups
- Adults of wide age range in breast
- Trauma in some but most do not
- Infants < 2y (cranial fasciitis)
Common sites:
- Upper extremity
- trunk
- chest
- back
- very uncommon in the breast
- head and neck
- outer table of the skull and contiguous soft
tissue of the scalp (cranial fasciitis)
- may extend to involve inner table into the
meninges
- small to medium-sized vessels (intravascular
fasciitis)
Gross features:
- subcutaneous usually
- subcutis, or muscle
- dermal location is rare
- breast parenchyma less common than subcutis
- 2 cm or less usually
- < 5 cm in the breast usually
- nodular
- poorly-defined margins, or well defined but not
encapsulated
- lytic lesion with sclerotic rims if skull is
involved (cranial fasciitis)
- may show cystic change centrally (breast)
Histologic features:
- may mimic sarcoma
- plump fibroblastic / myofibroblastic
cells
- pale eosinophilic cytoplasm
- plump vesicular nuclei
- hypercellular
- but usually at least partially discohesive and myxoid,
with a torn, feature or tissue culture-like character
- S or C-shaped fascicles often, or storiform sometimes
- plump, immature-appearing fibroblasts arranged
randomly
- or short, intersecting fascicles
- myxoid
stroma
- lymphocytes within stroma frequently
- extravasated
RBCs frequently
- osteoclast-like giant cells frequently
- granulation tissue appearance with numerous
small vessels
- cells vary in size and shape
- spindle to stellate
- conspicuous nucleoli
- mitotically active, but not atypical forms
- osseous metaplasia maybe
- keloidal
hyalinization maybe
Immunophenotype:
Marker:
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Sensitivity:
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Specificity:
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MSA (focal to diffuse)
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consistent
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SMA (focal to
diffuse)
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Caldesmon (neg)
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S100 (neg)
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Desmin (neg)
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rare
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Keratin (neg)
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CD34 (neg)
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typically
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Molecular features:
- MYH9-USP6 gene fusion
- t(17;22)(p13;q13)
- MYH9 (22q13)– encodes non-muscular myosin heavy
chain 9
- Involved in cell-shape maintenance, cell
motility, adhesion, differentiation and development
- USP6 (17p13) – deubiquitinating protease
- Cell trafficking, protein degratdation,
signaling and inflammation
- The few cases reported in the breast have shown
clonal cytogenetic aberrations (?MYH9-USP6 only
or others as well?)
Other features:
- Self-limiting (“transient neoplasia”)
- Recurrence after excision is rare but
occasionally observed after incomplete excision during the active growth
phase
- Spontaneous involution over 1-2 months in the
breast
- may
develop in areas of previous trauma (10-15%)
- develop suddenly and grow rapidly
- < 3-4 mo. Preoperative duration usually
- soreness, tenderness maybe
References:
- Robbins 2005
- Fletcher CDM et al., eds. WHO Classification of Tumors of Soft
Tissue and Bone, 4th ed. (2013)
- Lakhani SR et al., eds. WHO Classification of Tumours of the Breast, 4th ed. (2012)