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Peripheral nerve tumors, also called tumors of peripheral nerves or tumors of the peripheral nervous system, are a diverse category with a range of morphological characteristics and biological potential. [1] They are categorized as either benign or malignant peripheral nerve sheath tumors. [2] [3]
A malignant peripheral nerve sheath tumor (MPNST) is a form of cancer of the connective tissue surrounding peripheral nerves. Given its origin and behavior it is classified as a sarcoma. About half the cases are diagnosed in people with neurofibromatosis; the lifetime risk for an MPNST in patients with neurofibromatosis type 1 is 8–13%. [2]
Malignant melanotic nerve sheath tumor (previously known as melanotic schwannoma) is a rare aggressive peripheral nerve sheath tumor that typically develops in conjunction with spinal or visceral autonomic nerves, consisting uniformly of Schwann cells displaying melanocytic differentiation.
Malignant peripheral nerve sheath tumors are aggressive soft tissue sarcomas occurring on the exterior lining of nerves. [5] These nerves extend outward from the spinal cord to the rest of the body. Commonly, tumors develop promptly on extremities due to a mutation of the tumor suppressor, neurofibromin . [ 18 ]
In perineural invasion, cancer cells proliferate around peripheral nerves and eventually invade them. Cancer cells migrate in response to different mediators released by autonomic and sensory fibers. Tumor cells secrete CCL2 and CSF-1 to accumulate endoneurial macrophages and, at the same time, release factors that stimulate perineural invasion.
Schwannomas: Tumors arising from Schwann cells, which produce the myelin sheath surrounding peripheral nerves. A common subtype is the vestibular schwannoma (acoustic neuroma). [5] Neurofibromas: Benign tumors that grow on nerves, commonly associated with neurofibromatosis type I (NF1). [2]
For example, people with neurofibromatosis type I (also called von Recklinghausen disease, associated with alterations in the NF1 gene) are at an increased risk of developing soft-tissue sarcomas known as malignant peripheral nerve-sheath tumors.
The peripheral PNET (pPNET) is now thought to be virtually identical to Ewing sarcoma: "Current evidence indicates that both Ewing's sarcoma and PNET have a similar neural phenotype and, because they share an identical chromosome translocation, they should be viewed as the same tumor, differing only in their degree of neural differentiation.