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
      • volar aspect of forearm
    • 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)
        1. 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:

Sensitivity:

Specificity:

 MSA (focal to diffuse)

consistent

 

SMA (focal to diffuse)

 

 

Caldesmon (neg)

 

 

S100 (neg)

 

 

Desmin (neg)

rare

 

Keratin (neg)

 

 

CD34 (neg)

typically

 

 

Molecular features:

    • MYH9-USP6 gene fusion
      • t(17;22)(p13;q13)
      • MYH9 (22q13)– encodes non-muscular myosin heavy chain 9
        1. Involved in cell-shape maintenance, cell motility, adhesion, differentiation and development
      • USP6 (17p13) – deubiquitinating protease
        1. 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)