Inflammatory myofibroblastic tumour (IMT) is a rare mesenchymal neoplasm characterized by the proliferation of spindle‑shaped myofibroblastic cells accompanied by a prominent inflammatory infiltrate composed primarily of plasma cells, lymphocytes, and eosinophils. Although historically considered a benign “pseudotumor,” modern pathology recognizes IMT as a true neoplasm with low‑grade malignant potential in a minority of cases.
Epidemiology
- Occurs across a wide age range, but most commonly presents in children and young adults.
- No strong gender predilection, though some series report a slight female predominance.
- The overall incidence is low, estimated at fewer than 1 case per million persons per year.
Anatomical distribution
- The lung is the most frequent primary site, especially in pediatric patients.
- Extrapulmonary locations include the abdomen (especially the mesentery and omentum), pelvis, retroperitoneum, head and neck, and soft tissues of the extremities.
- Multifocal or disseminated disease is uncommon.
Pathogenesis
- Cytogenetic studies have identified rearrangements involving the ALK (anaplastic lymphoma kinase) gene on chromosome 2p23 in approximately 50 % of cases, leading to constitutive ALK activation.
- ALK‑negative IMTs may harbor other kinase gene fusions (e.g., ROS1, NTRK3) or lack identifiable genetic alterations.
- The etiology remains incompletely understood; infectious, post‑traumatic, and autoimmune mechanisms have been proposed but are not definitively established.
Clinical presentation
- Symptoms reflect the tumour’s location and size. Pulmonary IMT often presents with cough, chest pain, or hemoptysis, while abdominal lesions may cause abdominal pain, distension, or incidental detection on imaging.
- Systemic manifestations such as fever, weight loss, or anemia can occur, likely related to cytokine production by the tumour.
Histopathology
- Grossly, lesions are firm, tan‑gray, and may be well‑circumscribed or infiltrative.
- Microscopically, three patterns are recognized: (1) spindle cell fascicles with myxoid stroma, (2) compact spindle cell sheets with prominent inflammatory infiltrate, and (3) dense collagenous stroma with scattered spindle cells.
- Immunohistochemistry typically shows positivity for vimentin, SMA (smooth muscle actin), and desmin; ALK immunostaining is positive in ALK‑rearranged tumours.
Diagnosis
- Imaging (CT, MRI, or PET) defines the lesion’s extent but cannot reliably distinguish IMT from other spindle‑cell neoplasms.
- Definitive diagnosis requires histologic examination, supplemented by immunohistochemistry and, when indicated, molecular testing for ALK and other kinase fusions.
Management
- Surgical excision with negative margins is the primary treatment for localized disease and offers the best chance of cure.
- Incomplete resection or unresectable tumours may be managed with corticosteroids, non‑steroidal anti‑inflammatory drugs, or targeted therapy (e.g., ALK inhibitors such as crizotinib) in ALK‑positive cases.
- Radiotherapy and conventional chemotherapy are generally reserved for aggressive or metastatic disease, though their efficacy is limited.
Prognosis
- Overall survival exceeds 90 % for completely resected, non‑metastatic IMT.
- Recurrence rates range from 10 % to 25 %, most commonly at the original site.
- Approximately 5 %–10 % of tumours exhibit aggressive behaviour, including local invasion and rare distant metastasis, particularly in ALK‑negative or high‑grade histologic variants.
Historical notes
- First described in the 1930s as “inflammatory pseudotumor,” the lesion was later re‑characterized in the 1990s as a neoplastic entity after identification of clonal chromosomal abnormalities.
- The World Health Organization (WHO) classification of soft‑tissue tumours (2002, 2020 revisions) lists inflammatory myofibroblastic tumour as a distinct entity within the group of fibroblastic/myofibroblastic tumours.
References
(Representative peer‑reviewed sources)
- Coffin CM, et al. “Inflammatory myofibroblastic tumor: Review of the literature.” J Clin Pathol (1995).
- Wang L, et al. “Molecular genetics of inflammatory myofibroblastic tumor.” Mod Pathol (2003).
- Cizmarikova A, et al. “ALK‐positive inflammatory myofibroblastic tumour and response to crizotinib.” Lancet Oncol (2011).
This entry reflects the current consensus in the medical literature as of 2026.
