Surgical Pathology Criteria

Infantile Fibrosarcoma

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

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