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Soft tissue Tumors

Fibroblastic / myofibroblastic tumors

Fibrosarcoma of soft tissue - infantile

Reviewer: Komal Arora, M.D. (see Reviewers page)
Revised: 20 July 2012, last major update July 2012
Copyright: (c) 2003-2012, PathologyOutlines.com, Inc.

General
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● Resembles adult fibrosarcoma morphologically, but better prognosis
● Age cutoff between infantile and adult forms usually varies between 5 and 10 years

Epidemiology
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● Usually presents before age 2 years in axial regions or extremities with vary rapid growth
● Related to congenital mesoblastic nephroma, which has same translocation

Clinical description
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● 40-50% recur, but only rarely metastasizes
● Survival is 90%+

Case reports
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● Premature newborn with large facial mass (Arch Pathol Lab Med 2003;127:e281)
● Patient with shoulder mass clinically diagnosed as benign vascular lesion (Cutis 2012;89:61)

Treatment
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● Surgery and chemotherapy (J Pediatr Hematol Oncol 2002;24:722, Pediatr Blood Cancer 2009;53:23)

Gross description
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● May exceed 30 cm (grotesquely large compared to size of child) with tense erythematous and ulcerated overlying skin
● Firm to soft cut surface is fleshy, gray-tan with myxoid change, cystic degeneration, hemorrhage and necrosis

Gross images
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Fleshy white mass similar to adult fibrosarcoma

Micro description
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● Poorly circumscribed, lobulated mass of small to large spindled cells in fascicles or herringbone pattern with high cellularity, nuclear atypia and pleomorphism
● Increased mitotic figures, hemorrhage and necrosis
● Resembles adult fibrosarcoma
● May have prominent hemangiopericytoma-like areas, dystrophic calcification, extramedullary hematopoiesis
● Infiltrates adjacent soft tissue with irregular margins

Micro images
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Biphasic pattern with fibroblastic and cellular myxoid areas


High power of myxoid area


Infiltration of fat


Infiltration of muscle


Spindle cells


Plump cells have granular chromatin

   
Less cellular tumor which overlaps with infantile fibromatosis, although it almost never metastasizes


Areas of variable cellularity

   
Tumor with features of infantile fibrosarcoma and congenital mesoblastic nephroma

Leg tumor #1, #2, #3

Positive stains
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● Vimentin
● Variable focal smooth muscle actin, desmin, S100 and CD34

Electron microscopy description
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● Fibroblastic and myofibroblastic features

Molecular
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● 70% have t(12;15)(p13;q26), causes ETV6-NTRK3 gene fusion transcript (ETS variant gene 6 and neurotrophic tyrosine receptor kinase type 3) detectable by FISH (Mod Pathol 2001;14:1246) or RT-PCR (Am J Surg Pathol 2000;24:937, Am J Clin Pathol 2001;115:348)
● Similar translocation also present in secretory breast carcinoma (Mod Pathol 2009;22:291)
● Also trisomy 8, 11, 17 and 20

Molecular images
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Ideogram of fusion transcript and FISH

Differential diagnosis
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● Adult type fibrosarcoma: usually age 10+, no t(12;15)
● Infantile fibromatosis: no pleomorphism, no mitotic figures, no t(12;15)
● Myofibromatosis: myofibroblastic features, no t(12;15) (Pediatr Dev Pathol 2008;11:355)

Additional references
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● Stanford University

End of Soft Tissue Tumors > Fibroblastic / myofibroblastic tumors > Fibrosarcoma of soft tissue - infantile

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