Stanford School of Medicine
Surgical Pathology Criteria
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Infantile Fibrosarcoma


  • Malignant neoplasm composed of uniform, cytologically malignant spindled fibroblasts or myofibroblasts occurring under age 10

Alternate/Historical Names

  • Congenital fibrosarcoma
  • Desmoplastic fibrosarcoma of infancy
  • Juvenile fibrosarcoma
  • Medullary fibromatosis of infancy

Diagnostic Criteria

  • Under age 10 years
  • Uniform spindle cells
    • Elongate nuclei
    • Scant cytoplasm
    • May have round cell areas
      • Must have conventional areas also
  • Hyperchromatic, granular chromatin
    • Nucleoli may be multiple and prominent
    • Mitotic figures usually frequent and abnormal
  • Broad cellular fascicles
    • Frequent herringbone pattern (intersection of fascicles at acute angles)
    • May be long sweeping fascicles
  • Scant stroma
    • Stroma may be focally myxoid
    • Must have conventional areas also
    • May have dilated congested vessels
    • May have hemangiopericytic vessels
    • Frequently scattered chronic inflammatory cells
  • Immunohistochemistry must not show evidence of specific differentiation
    • Actin variable
    • Desmin, CD34, S100 negative
  • See separate entities:

    Richard L Kempson MD
    Robert V Rouse MD
    Department of Pathology
    Stanford University School of Medicine
    Stanford CA 94305-5342

    Original posting: October 15, 2007
    Last Update: January 26, 2008


Supplemental studies


  • Fibrosarcoma by definition must not show evidence of specific differentiation
  • Actin (smooth muscle or muscle specific) may be seen in about 1/3 of cases
  • Other markers show only focal cell reactivity at most
    • Keratin, desmin, S100, CD34


  • t(12;15) (p13;q26) present in most cases
    • Involves NTRK3 tyrosine kinase receptor
    • Same translocation has been identified in congenital mesoblastic nephroma
  • Cytogenetic confirmation required if patient >2 years of age


Differential diagnosis

Myofibroma Infantile Fibrosarcoma
Random spindle cell pattern Fascicular pattern
Biphasic mature and immature areas No biphasic pattern
Atypical mitotic figures rare Atypical mitotic figures common


Infantile Fibromatosis Infantile Fibrosarcoma
Mild to moderate cellularity Usually more cellular
Fine chromatin Usually clumped chromatin
Rarely > 5 mitotic figures per HPF Usually > 5 mitotic figures per HPF
Atypical mitotic figures rare Atypical mitotic figures common
Variably collagenous stroma Little collagen in stroma
No herringbone pattern Frequent herringbone pattern
Hemorrhage and necrosis rare Frequent hemorrhage and necrosis
Muscle fibers preserved Muscle fibers destroyed
Lacks t(12;15) t(12;15) in most cases
Distinction between grade I fibrosarcoma and desmoid fibromatosis may not always be clear


Infantile Fibrosarcoma Monophasic Synovial Sarcoma
May have extensive herringbone pattern Herringbone pattern usually only focal
Keratin, EMA negative or at most focal Keratin, EMA usually positive
No ropy collagen Ropy collagen frequent
Calcification rare Calcification common
Elongate nuclei Plump nuclei
Chromatin not stippled Stippled chromatin
t(12;15) usually present SYT-SST gene fusion present
Both may have hemangiopericytomatous vessels


Embryonal Rhabdomyosarcoma Infantile Fibrosarcoma
Desmin and myogenin positive Desmin and myogenin negative
No areas of conventional fibrosarcoma Areas of conventional fascicular pattern present
Infantile fibrosarcoma may have round cell areas reminiscent of rhabdomyosarcoma


Leiomyosarcoma of Deep Soft Tissue or Retroperitoneum Adult or Infantile Fibrosarcoma
Frequently desmin positive Desmin negative
Frequently pleomorphic Uniform
May occur in retroperitoneum or pelvis Rare in retroperitoneum and pelvis
Lacks t(12;15) t(12;15) usually present in infantile fibrosarcoma
Distinction may be arbitrary in some cases but desmin positive neoplastic cells exclude fibrosarcoma


Dermatofibrosarcoma Protuberans Adult or Infantile Fibrosarcoma
CD34 positive CD34 negative
Storiform pattern Fascicular, herringbone pattern
Involves dermis and subcutaneous tissue Virtually always in deep soft tissue
DFSP may dedifferentiate with a fibrosarcoma pattern
If fibrosarcoma occurs in the dermis or subcutaneous tissue, it is usually dedifferentiated DFSP


Primitive Peripheral Neuroectodermal Tumor Infantile Fibrosarcoma
CD99 positive CD99 negative
No areas of conventional fibrosarcoma Areas of conventional fascicular pattern present
Various translocations involving 22q12 t(12;15) (p13;q26) present in most cases
Infantile fibrosarcoma may have round cell areas reminiscent of PNET


Malignant Peripheral Nerve Sheath Tumor Adult or Infantile Fibrosarcoma
May be S100 positive (50%) S100 negative
May be pleomorphic Uniform
May arise from nerve or neurofibroma No relation to nerve or neurofibroma
May arise in von Recklinghausen disease Not related to von Recklinghausen disease
Lacks t(12;15) t(12;15) usually present in infantile fibrosarcoma


Cellular Fibroma of Tendon Sheath Adult or Infantile Fibrosarcoma
Common in hands Rare in hands in adults but may involve hands in infantile version
Rare >2 cm Frequently >4 cm
Cytologically bland Cytologically atypical
No atypical mitotic figures Atypical mitotic figures may be seen
Smooth muscle actin strongly positive Actin variable
Lacks t(12;15) t(12;15) present in most infantile cases


  • Under age 10 by definition
    • Most <2 years
    • May be congenital
    • Few between 2 and 10 years
  • May involve deep soft tissues or subcutaneous tissues
    • Most common in extremities
    • Very rare in retroperitoneum and mediastinum
  • Behavior under age 5 years
    • Recurrence rate about 25%
    • Metastatic rate <10%


Grading does not predict outcome

Use TNM Staging

The surgical pathology report should contain or address the following:

    • Location
    • Type of resection or biopsy
    • Histologic diagnosis
    • Managerial category III (Local recurrence common; Metastasis occurs)
    • Extent of tumor cell necrosis
    • Stage
    • Size
    • Depth (dermis, subcutis, below fascia, body cavity)
    • Margins
      • Involved
      • Not involved
        • If under 2 cm give all such distances and sites
        • If over 2 cm give minimum distance and site
    • Results of supplementary studies if performed
    • Relationship to other specimens from the same patient


Predominantly fibrous soft tissue sarcomas

Predominantly Pediatric Fibrous Lesions

Lesions that may demonstrate a prominent hemangiopericytoma-like vascular pattern


  • Kempson RL, Fletcher CDM, Evans HL, Henrickson MR, Sibley RS. Tumors of the Soft Tissues, Atlas of Tumor Pathology, AFIP Third Series, Fascicle 30, 2001
  • Fletcher CDM, Unni KK, Mertens F. Pathology and Genetics of Tumours of Soft Tissue and Bone, World Health Organization Classification of Tumours 2002
  • Weiss SW, Goldblum JR. Enzinger and Weiss's Soft Tissue Tumors, 4th edition, 2001
  • Coffin CM, Jaszcz W, O'Shea PA, Dehner LP. So-called congenital-infantile fibrosarcoma: does it exist and what is it? Pediatr Pathol. 1994 Jan-Feb;14(1):133-50.
  • Kodet R, Stejskal J, Pilat D, Kocourkova M, Smelhaus V, Eckschlager T. Congenital-infantile fibrosarcoma: a clinicopathological study of five patients entered on the Prague children's tumor registry. Pathol Res Pract. 1996 Aug;192(8):845-53; discussion 854-5.
  • Coffin CM, Dehner LP. Fibroblastic-myofibroblastic tumors in children and adolescents: a clinicopathologic study of 108 examples in 103 patients. Pediatr Pathol. 1991 Jul-Aug;11(4):569-88.
  • Bourgeois JM, Knezevich SR, Mathers JA, Sorensen PH. Molecular detection of the ETV6-NTRK3 gene fusion differentiates congenital fibrosarcoma from other childhood spindle cell tumors. Am J Surg Pathol. 2000 Jul;24(7):937-46.
  • Sheng WQ, Hisaoka M, Okamoto S, Tanaka A, Meis-Kindblom JM, Kindblom LG, Ishida T, Nojima T, Hashimoto H. Congenital-infantile fibrosarcoma. A clinicopathologic study of 10 cases and molecular detection of the ETV6-NTRK3 fusion transcripts using paraffin-embedded tissues. Am J Clin Pathol. 2001 Mar;115(3):348-55.
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