Definition/General
Introduction:
Inflammatory myofibroblastic tumor is an intermediate soft tissue tumor
Shows myofibroblastic proliferation with inflammation
Has potential for recurrence
FNAC shows spindle cells and inflammatory cells.
Origin:
Arises from myofibroblasts
Associated with chronic inflammation
Can occur in any anatomic site
Reactive vs neoplastic debate
Shows clonal genetic alterations.
Classification:
WHO classification: Intermediate (rarely metastasizing)
Previously: Inflammatory pseudotumor
Plasma cell granuloma
Pseudosarcomatous myofibroblastic proliferation.
Epidemiology:
Peak incidence 1st-2nd decades
Equal gender distribution
Children and young adults
Lung most common site
Extrapulmonary sites increasingly recognized.
Clinical Features
Presentation:
Mass lesion
Cough and dyspnea (pulmonary)
Fever (25%)
Weight loss
Malaise
Site-specific symptoms.
Symptoms:
Constitutional symptoms
Fever and weight loss
Mass effect
Pain (variable)
Anemia
Elevated ESR/CRP.
Risk Factors:
Previous infection
Trauma
Surgery
Foreign body
Autoimmune conditions
EBV association (some cases).
Screening:
Clinical examination
Laboratory tests (inflammatory markers)
Imaging (CT/MRI)
FNAC/Biopsy
Molecular studies.
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Gross Description
Appearance:
Well-circumscribed mass
Firm, gray-white
Whorled cut surface
Variable consistency
Multinodular
No necrosis typically.
Characteristics:
Pseudocapsule
Fibrous appearance
Gray-white color
Firm consistency
Homogeneous or heterogeneous
Calcification rare.
Size Location:
Lung (40%)
Abdomen (25%)
Soft tissues (20%)
Other sites (15%)
Size: Variable 2-15 cm
Mesenteric location common.
Multifocality:
Usually solitary
Multifocal rare
Local recurrence (15-37%)
Metastases very rare (<5%)
Complete excision important.
Microscopic Description
Histological Features:
FNAC shows spindle-shaped myofibroblasts
Mixed inflammatory infiltrate
Plasma cells, lymphocytes, eosinophils
Varying cellularity
Collagen bundles.
Cellular Characteristics:
Spindle myofibroblasts
Oval to elongated nuclei
Moderate cytoplasm
Plasma cells prominent
Mixed inflammatory cells
Variable atypia.
Architectural Patterns:
Fascicular arrangement
Storiform pattern
Inflammatory background
Loose to dense
Myxoid areas
Hyalinized collagen.
Grading Criteria:
Intermediate malignancy
Cellular atypia variable
Mitotic activity low to moderate
Rare metastases
Local recurrence potential
Complete excision curative.
Immunohistochemistry
Positive Markers:
Smooth muscle actin - positive
Muscle-specific actin - positive
Vimentin - positive
ALK - positive (50%)
Desmin - focal positive
Calponin - positive.
Negative Markers:
Cytokeratin - negative
S-100 - negative
CD34 - negative
MyoD1 - negative
CD117 - negative
EMA - negative.
Diagnostic Utility:
ALK positivity supports diagnosis (50% cases)
Smooth muscle markers confirm myofibroblastic nature
Inflammatory markers for plasma cells
Ki-67 low to moderate.
Molecular Subtypes:
ALK-positive IMT: Various ALK fusions
ALK-negative IMT: ROS1, PDGFRB rearrangements
All types: Myofibroblastic markers positive.
Molecular/Genetic
Genetic Mutations:
ALK rearrangements (50%)
TPM3-ALK, TPM4-ALK common
ROS1 rearrangements (ALK-negative)
PDGFRB rearrangements
NTRK3 fusions (rare).
Molecular Markers:
ALK protein overexpression
Clonal rearrangements
Inflammatory pathways activated
PI3K/AKT pathway
Low mutational burden.
Prognostic Significance:
ALK-positive: Better defined entity
Complete excision: Excellent prognosis
Incomplete excision: Higher recurrence
Metastases rare (<5%)
Children: Better outcome.
Therapeutic Targets:
Complete surgical excision
ALK inhibitors (crizotinib) for unresectable
Anti-inflammatory agents
Corticosteroids
Targeted therapy based on molecular profile.
Differential Diagnosis
Similar Entities:
Leiomyosarcoma
Fibrosarcoma
Gastrointestinal stromal tumor
Spindle cell carcinoma
Solitary fibrous tumor
Inflammatory processes.
Distinguishing Features:
IMT: ALK+ (50%), inflammatory infiltrate, intermediate behavior
Leiomyosarcoma: Desmin+, high-grade atypia
Fibrosarcoma: No inflammation
GIST: CD117+, ALK- usually
SFT: CD34+.
Diagnostic Challenges:
Reactive vs neoplastic
ALK-negative cases
Limited tissue in FNAC
Inflammatory background masking cells
Site-specific variants.
Rare Variants:
Epithelioid IMT
Myxoid IMT
Dedifferentiated IMT
IMT with ganglion-like cells.
Sample Pathology Report
Template Format
Sample Pathology Report
Complete Report: This is an example of how the final pathology report should be structured for this condition.
Specimen Information
Fine needle aspiration from [site], [size] cm mass
Clinical History
[age]/[sex] with [duration] history of mass at [site]. [Constitutional symptoms if present].
Microscopic Examination
Smears show spindle-shaped myofibroblasts admixed with inflammatory cells including plasma cells, lymphocytes, and eosinophils. Variable cellularity and mild to moderate nuclear atypia.
Immunocytochemistry
SMA: Positive, ALK: [Positive/Negative], Desmin: Focal positive, S-100: Negative
Molecular Studies
ALK rearrangement: [result], [other molecular studies if performed]
Cytological Diagnosis
Cytological features consistent with INFLAMMATORY MYOFIBROBLASTIC TUMOR
Comments
Intermediate soft tissue tumor with potential for local recurrence. Complete surgical excision recommended. Molecular studies helpful for targeted therapy options.