This category is immensely broad and contains a large number of benign processes in infants and children. Of important to oncology are solitary fibrous tumours, inflammatory myofibroblastic tumours, myofibroblastic sarcoma, myxoinflammatory fibroblastic sarcoma, fibrosarcoma, myxofibrosarcoma and low grade fibromyxoid sarcoma.
Solitary fibrous tumours occur most commonly between the ages of 20-70.
Inflammatory myofibroblastic tumour, also known as inflammatory pseudotumour, occurs in children and adolescents. It can occur at any site in the body, but most commonly in the lung (where it represents the most common benign tumour of children and adolescents), omentum and mesentery.
The epidemiology of myofibrosarcoma is not well understood.
Inflammatory myxofibroblastic sarcoma is a rare malignancy of the 4th and 5th decades, most commonly in women.
Fibrosarcoma is an uncommon form of soft tissue sarcoma (1-3% in total), it is more common in older individuals but may occur in children (infantile fibrosarcoma) where it has a better prognosis.
Myxofibrosarcoma is a common sarcoma of the elderly.
Low grade fibromyxoid sarcoma is a rare tumour of younger adults. 20% occur in children.
Solitary fibrous tumour can occur at any site in the body, although most occur in the superficial fascia.
Inflammatory myofibroblastic tumour often occurs in the lung, omentum and mesentery but can occur at any other site including the CNS.
Low grade myofibroblastic sarcoma can occur at any site, but most often in the head and neck and extremities.
Inflammatory myxofibroblastic sarcoma has a predilection for the distal extremeties (66% of cases).
Fibrosarcoma in adults may occur at a variety of sites including the head and neck, trunk and limbs. Retroperitoneal fibrosarcoma is distinctly rare. In children, lesions frequently arise in the distal extremities.
Myxofibrosarcoma almost always occurs in the extremities (particularly the lower limb girdle).
Low grade fibromyxoid sarcomas typically occur in the extremities but can occur at any site.
Aetiology and Pathogenesis
The aetiology of these tumours is unknown.
Solitary fibrous tumour and inflammatory myofibroblastic tumour are mostly benign conditions. A minority of solitary fibrous tumours behave aggressively with high rates of local recurrence and risk of metastases. Inflammatory myofibroblastic tumours recur in 20-30% of cases but very rarely metastasise.
The low grade fibre/myofibrosarcomas have a relatively high rate of local recurrence (30-50%) but low rates of metastases. Fibrosarcoma and myxofibrosarcoma have a higher rate of metastasis and local recurrence.
Given their propensity to develop at unusual sites, the presentation of these tumours can be highly variable. Those that develop in the limbs and distal extremities tend to present with an enlarging mass that is usually not painful.
Solitary Fibrous Tumour
The tumour is typically well circumscribed with a partial capsule. The cut surface is white and nodular. Microscopically, the malignant cells are round to spindle shaped with a small amount of cytoplasm. The cellularity varies throughout the tumour and there are hyalinised vessels and collagen fibres. Most tumours stain positively for CD34. Genetic findings are variable.
Inflammatory myofibroblastic tumour
Inflammatory myofibroblastic tumours are white to tan with a whorled cut surface. Microscopically they are formed by three cell populations, fibroblasts, myofibroblasts and inflammatory cells that have a variety of arrangements. Genetic studies demonstrate a high number of cases with rearrangements of the ALK gene on chromosome 2.
Low grade myofibrosarcoma
Myxofibrosarcoma is typically pale with a whorled cut surface. Microscopically the tumour is formed by spindle cells with moderate anaplastic change (eg. nuclear pleomorphism). Staining for actin, desmin or both is common. Genetic features are unclear.
Myxoinflammatory fibroblastic Sarcoma
Fibrosarcoma is a rare sarcoma (1-3%). It has a white to tan colour macroscopically and is usually firm. Microscopically, it consists of spindle cells arranged in a herringbone pattern.
Fibrosarcomas stain for vimentin. Genetic changes are complex.
Staging / Classification
TNM or other staging system if relevant