Soft tissue

Fibroblastic / myofibroblastic

Inflammatory myofibroblastic tumor

Editorial Board Members: Jose G. Mantilla, M.D., Borislav A. Alexiev, M.D.
Carina Dehner, M.D., Ph.D.
Louis P. Dehner, M.D.

Last author update: 9 July 2021
Last staff update: 9 July 2021

Copyright: 2002-2024,, Inc.

PubMed Search: Inflammatory myofibroblastic tumor[title] soft tissue pathology

Carina Dehner, M.D., Ph.D.
Louis P. Dehner, M.D.
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Cite this page: Dehner C, Dehner L. Inflammatory myofibroblastic tumor. website. Accessed February 23rd, 2024.
Definition / general
  • Histologically distinctive myofibroblastic spindle cell neoplasm of borderline malignancy, classically featuring an intermixture of plasma cells and lymphocytes
Essential features
  • Myofibroblastic spindle cell neoplasm of borderline malignancy
  • Myofibroblastic spindle cells without overt cytologic atypia, interspersed by more or less prominent lymphoplasmacytic infiltrates
  • Up to 60% of cases show ALK rearrangement and will be positive for ALK1 IHC
  • Patients may present with constitutional symptoms (fever, night sweats, weight loss)
  • Epithelioid inflammatory myofibroblastic sarcoma is a distinct, highly aggressive variant that is predominantly intra-abdominal and is associated with a worse outcome
  • Inflammatory pseudotumor; inflammatory myofibrohistiocytic proliferation; plasma cell granuloma; inflammatory fibrosarcoma (obsolete terms, not recommended)
ICD coding
  • ICD-O: 8825/1 - Inflammatory myofibroblastic tumor
  • ICD-10: D48.9 - Neoplasm of uncertain behavior, unspecified
  • ICD-11: 2B53.Y & XH66Z0 - Other specified fibroblastic or myofibroblastic tumor, primary site and myofibroblastic tumor, NOS
  • Wide age range but most common in children and young adults
  • Extrapulmonary IMTs show predilection for children, with mean age of ~10 years (Semin Diagn Pathol 1998;15:85)
Clinical features
  • Site specific symptoms
  • Intra-abdominal tumors associated with increased abdominal girth, possibly symptoms of obstruction
  • Some patients (~33%) will present with systemic symptoms, such as fever, night sweats, weight loss (thought to be related to cytokine release) (Cytokine 2008;44:293)
  • Tissue sampling and histological examination
  • Some patients have laboratory abnormalities (elevated erythrocyte sedimentation rate [ESR], hypochromic, normocytic anemia, thrombocytosis, hypergammaglobulinemia), which resolve soon after surgical resection (Cancer 1993;72:2042, Semin Diagn Pathol 1998;15:85)
Radiology description
  • Nonspecific radiology findings; ultrasound may show hypoechoic or hyperechoic mass(es) with ill or well defined borders; increased vascularity on Doppler studies
  • CT may show a homogeneous or heterogenous lesion with variable enhancement on delayed acquisitions due to fibrosis; calcification(s) seen in 15 - 25% of lung lesions in children, while rare in adult patients (Insights Imaging 2015;6:85, Radiology 1998;206:511)
  • MRI shows low signal intensity on T1 and T2 weighted sequences (Insights Imaging 2015;6:85)
Radiology images

Contributed by Carina Dehner, M.D., Ph.D.

Upper lobe mass

Upper lobe mass cross sectional imaging

Prognostic factors
  • Variable; generally good prognosis but up to 35% may recur and rare cases of distant metastasis have been reported
  • Adverse factors: intra-abdominal location, epithelioid variant
  • No established correlation of tumor size, mitotic rate, cellularity, necrosis and atypia with outcome in conventional IMT; however, ALK positive IMTs are less likely to recur and may have less aggressive behavior (Am J Surg Pathol 2007;31:509)
Case reports
  • Surgical resection (re-excision of recurrences)
  • Treatment with specific tyrosine kinase inhibitors, such as crizotinib (N Engl J Med 2010;363:1727)
Gross description
  • Circumscribed, solid mass with rubbery cut surface
  • May present with calcifications
  • May present as multiple nodules (same anatomic site) in 33% of cases
  • Size ranges from 1 to 20 cm (median: 5 - 6 cm)
Gross images

Contributed by Carina Dehner, M.D., Ph.D.

Well circumscribed, firm white

Microscopic (histologic) description
  • Myofibroblastic spindle cell proliferation with mixed inflammation (lymphocytes, plasma cells and eosinophils)
  • Number of mitotic figures varies, atypical figures can be seen
  • Significant pleomorphism should be viewed with concern, may not fit with diagnosis of IMT
  • Variety of histologic patterns sometimes seen
    • Loosely arranged myxoid or hyaline stroma, spindle to stellate cells and admixed inflammatory cells (nodular fasciitis-like)
    • Storiform or fascicular growing elongated spindle cells without overt hyperchromasia or cytologic atypia, associated with prominent lymphoplasmacytic infiltrate
    • Hypocellular, scar-like pattern with occasional metaplastic bone or associated calcifications
  • Some tumors may show ganglion-like cells
  • Epithelioid variant predominantly composed of plump round to epithelioid cells with vesicular chromatin, large, prominent nucleoli and amphiphilic to eosinophilic cytoplasm; a prominent neutrophilic component and abundant myxoid stroma are common (Am J Surg Pathol 2011;35:135)
  • Reference: Goldblum: Enzinger and Weiss's Soft Tissue Tumors: Expert Consult, 7th Edition, 2019
Microscopic (histologic) images

Contributed by Carina Dehner, M.D., Ph.D.

Variable cellularity

Myofibroblasts and inflammatory cells

Short fascicles of spindle cells

Myofibroblasts without overt atypia

Eosinophilic cytoplasm

Ganglion-like cells


Desmin IHC

Positive stains
Negative stains
Electron microscopy description
  • Myofibroblasts and fibroblasts
Molecular / cytogenetics description

Inflammatory myofibroblastic tumor

Sample pathology report
  • Lung, right upper lobe, pneumonectomy:
    • Inflammatory myofibroblastic tumor, ALK positive, present at bronchial and vascular margins (see comment)
    • Comment: Sections of the right lobe show a circumscribed spindle cell neoplasm with a prominent inflammatory component. The tumor has replaced the lung parenchyma and is continuous with the right upper lobe bronchus with partial destruction of the bronchial cartilage. The bronchial and vascular margins are involved by tumor. Immunohistochemical stains show that tumor cells are diffusely positive for vimentin, SMA and ALK, while negative for IgG and IgG4. In summary, the morphological and immunohistochemical features support the diagnosis of inflammatory myofibroblastic tumor.
Differential diagnosis
Board review style question #1

Which of the following is true about the inflammatory myofibroblastic tumor?

  1. Average age is 60 years or older
  2. It can be easily classified on imaging
  3. It is known to have USP6 rearrangement
  4. It never metastasizes
  5. Its aggressive variant shows perinuclear or nuclear membrane staining for ALK
Board review style answer #1
E. Its aggressive variant (epithelioid inflammatory myofibroblastic tumor) shows distinct, perinuclear or nuclear membrane staining for ALK.

Comment Here

Reference: Inflammatory myofibroblastic tumor
Board review style question #2
Which of the following genes may show a molecular abnormality in inflammatory myofibroblastic tumor?

  1. CTNNB1
  2. MYC
  3. NOTCH3
  4. ROS1
  5. USP6
Board review style answer #2
D. ROS1. ALK negative IMTs may show ROS1 alterations.

Comment Here

Reference: Inflammatory myofibroblastic tumor
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