Home   Chapter Home   Jobs   Conferences   Fellowships   Books


Soft tissue Tumors

Fibroblastic / myofibroblastic

Inflammatory myofibroblastic tumor of soft tissue

Reviewer: Komal Arora, M.D. (see Reviewers page)
Revised: 18 July 2012, last major update July 2012
Copyright: (c) 2003-2012, PathologyOutlines.com, Inc.


● Tumor of myofibroblasts with plasma cells, lymphocytes and eosinophils
● Also called inflammatory fibrosarcoma, inflammatory pseudotumor, plasma cell granuloma
● See also discussions in these chapters: Bladder, Bone, Breast nonmalignant, CNS tumor, Colon tumor, Eye (orbit), Heart tumor, Kidney tumor, Liver tumor, Lung tumor, Lymph node-not lymphoma, Mediastinum, Pancreas, Salivary glands, Small bowel, Spleen, Thyroid gland
● Retroperitoneum (omentum) and mesentery in children and young adults (mean age 10 years)
● Also lung, GI, GU, other sites

Poor prognostic factors:
● Abdominal or pelvic sites, ALK negative (Am J Surg Pathol 2007;31:509)

Clinical description

● 1/3 have associated fever, growth failure, malaise, weight loss, anemia, thrombocytosis, polyclonal hyperglobulinemia and elevated sedimentation rate
● Symptoms disappear after excision of mass (J Korean Med Sci 2002;17:699)

Case reports

● 6 year old boy with abdominal wall tumor (Surg Today 2007;37:352)
● 7 year old girl whose abdominopelvic tumor has t(1;2)(q21;p23) (Arch Pathol Lab Med 2006;130:1042)
● 18 year old man with omental tumor and bone marrow involvement (Arch Pathol Lab Med 2003 Jul;127:865)
● 46 year old woman with retroperitoneal tumor (World J Surg Oncol 2005;3:66)
● 63 year old man with mesenteric tumor (World J Gastroenterol 2007;13:3645)


● Excision (J Pediatr Surg 2005;40:1581)
● 25-35% recur, rare metastases (or may be evidence of multifocality)

Gross description

● Circumscribed, not encapsulated
● White tan mass with whorled fleshy or myxoid cut surface
● May have focal hemorrhage, necrosis or calcification, mean 6 cm

Gross images

19 cm mesenteric tumor (fig 2-4)

Micro description

● Myofibroblastic and fibroblastic spindle cells with inflammatory infiltrate of lymphocytes, plasma cells, eosinophils, histiocytes
● Background of abundant blood vessels
● Mixture of three patterns:
  (1) resembling nodular fasciitis with elongated myofibroblasts containing abundant eosinophilic cytoplasm and vesicular nuclei, loose myxoid stroma with neutrophils, lymphocytes and eosinophils, but few plasma cells;
  (2) cellular with spindled myofibroblasts and fibroblasts in more compact stroma, arranged as islands surrounded by fibromyxoid stroma with prominent plasma cells and mitotic figures;
  (3) densely hyalinized stroma with few spindle cells, few plasma cells or lymphocytes
● May have ganglion-cell like myofibroblasts
● All 3 patterns have no nuclear pleomorphism, no atypical mitotic figures
Malignant behavior - associated with highly atypical polygonal cells with oval nuclei, prominent nucleoli, Reed-Sternberg like cells, atypical mitotic figures

Micro images

Typical appearance of spindled myofibroblastic cells and inflammatory infiltrate

Inflammation obscures the underlying myofibroblastic proliferation

Spindle cells are evident at high power

Tumor with more fibrous stroma

Myofibroblasts and inflammatory cells

Various images

Retroperitoneal tumor #1, #2, #3, #4

H&E, ALK1 and p80

Virtual slides

Inflammatory myofibroblastic tumor

Electron microscopy description

● Myofibroblastic cells and activated fibroblasts

Electron microscopy images

Figure b: filamentous bundles, attachment densities, pinocytotic vesicles and basal lamina

Positive stains

● Vimentin (diffuse, strong), usually alpha smooth muscle actin, muscle specific actin and calponin (Hum Pathol 2008;39:846)
● ALK1 / p80 in 40%, but not specific (Mod Pathol 2002;15:931)
● Keratin and desmin in 1/3

Negative stains

● S100, CD117, HHV8 (Mod Pathol 2007;20:995)
● CD34, h-caldesmon


● Clonal abnormalities of 2p23 (Cancer Res 1999;59:2776) including t(2;5)(p23;q35) involving ALK and NPM
● Also t(2;17)(p23;q23) involving ALK and CLTC (Am J Pathol 2001;159:411) and t(2;19)(p23;p13.1) involving ALK and TPM4 (Am J Pathol 2000;157:377)
● Associated with ALK deregulation and younger patients
● See Atlas of Genetics

Molecular images

t(2;5) karyotype

ALK translocation is indicated by separation of green and orange probes of ALK gene in inflammatory myofibroblastic tumor (a), but not leiomyosarcoma (b)

ALK staining, FISH and karyotype


Differential diagnosis

● Calcifying fibrous pseudotumor: calcification, no myofibroblastic proliferation, actin negative (Mod Pathol 2001;14:784)
● Nodular fasciitis: smaller size, older patients, less inflammation
● Low grade myofibroblastic sarcoma: more uniform appearance with higher cellularity, more prominent hyperchromasia, more infiltrative, ALK (Hum Pathol 2008;39:846)
● IgG4 related sclerosing lesion: IgG4+ plasma cells and the ratio of IgG4+/IgG+ plasma cells is lower in IMT
● The presence of obstructive phlebitis
● Absence of ALK (Mod Pathol 2011;24:606, Am J Surg Pathol 2009;33:1330)

End of Soft Tissue Tumors > Fibroblastic / myofibroblastic > Inflammatory myofibroblastic tumor of soft tissue

This information is intended for physicians and related personnel, who understand that medical information is often imperfect, and must be interpreted in the context of a patient's clinical data using reasonable medical judgment. This website should not be used as a substitute for the advice of a licensed physician.

All information on this website is protected by copyright of PathologyOutlines.com, Inc. Information from third parties may also be protected by copyright. Please contact us at copyrightPathOut@gmail.com with any questions (click here for other contact information).