The term “nerve cancer” generally refers to tumors developing in or around the peripheral nervous system, which includes all nerves outside the brain and spinal cord. While many nerve tumors are benign, the most aggressive type is the malignant peripheral nerve sheath tumor (MPNST). MPNSTs are abnormal growths arising from the protective tissue layers, known as the nerve sheath, that insulate nerve fibers. This form of cancer is classified as a soft tissue sarcoma, known for its rapid growth and potential to spread.
Classifying Nerve Tumors: Types and Origins
Malignant Peripheral Nerve Sheath Tumors (MPNSTs) represent the cancerous extreme of nerve tumors, originating directly from the cells that form the nerve’s protective covering. Derived from Schwann cells or other pluripotent cells, they are a rare, highly aggressive form of soft tissue sarcoma. MPNSTs can arise spontaneously, but 25% to 50% are associated with the inherited disorder Neurofibromatosis Type 1 (NF1).
The vast majority of nerve sheath tumors are benign, including Neurofibromas and Schwannomas, which are common in NF1 patients. Neurofibromas, particularly the complex plexiform type, have an 8% to 13% lifetime risk of malignant transformation into an MPNST. These non-cancerous tumors serve as precursor lesions requiring careful monitoring for accelerated growth. The NF1 gene mutation disrupts a tumor suppressor protein, driving the development and malignant transformation of these tumors.
Recognizing the Signs: Common Symptoms
The presence of a nerve tumor often becomes apparent when the growth compresses the nerve or surrounding tissues. A common initial sign is a palpable mass or lump beneath the skin, which may feel fixed or tender. These tumors are most frequently located in the deep tissues of the arms, legs, or torso, where the peripheral nerves are large.
Pain is a characteristic symptom, especially if it is persistent, progressive, and not relieved by typical medication. This localized pain often worsens at night or presents as a shooting, electric-shock sensation. As the tumor grows, it causes neurological deficits in the area served by the affected nerve.
Nerve compression frequently leads to paresthesia, including tingling, burning, or numbness in the limb. Progressive muscle weakness or atrophy can also occur, making movement difficult. Rapid worsening of these symptoms may suggest a malignant transformation or a fast-growing MPNST.
Diagnostic Procedures
The evaluation process begins with a comprehensive physical and neurological examination to assess sensory function, muscle strength, and reflexes. The physician manually checks for the presence of any masses, their size, and whether they are mobile or fixed. Imaging studies are then employed to visualize the tumor and determine its relationship to the nerve and other structures.
Magnetic Resonance Imaging (MRI) is the most effective imaging modality, providing detailed, three-dimensional views of the soft tissues to delineate the tumor’s size and location. A CT scan may assess spread to the lungs or bone involvement, though it is less effective for soft tissue characterization. A Positron Emission Tomography (PET) scan is sometimes utilized for patients with known precursor lesions to help distinguish between a benign growth and a malignant transformation based on metabolic activity.
A definitive diagnosis requires a tissue biopsy, where a small sample of the tumor is removed, often using a needle guided by ultrasound or CT imaging. A pathologist examines the tissue under a microscope to confirm the cell type, determine the tumor’s grade, and confirm malignancy. This step is essential for accurate classification and treatment planning.
Standard Treatment Modalities
The primary treatment strategy for malignant peripheral nerve sheath tumors is aggressive surgical resection, aiming for complete removal, known as an R0 resection. This involves removing the tumor along with a surrounding margin of healthy tissue to minimize local recurrence risk. The challenge is performing this wide excision while preserving the function of the involved nerve, often requiring a specialized surgical approach.
Radiation therapy is frequently employed in combination with surgery. It may be given before surgery (neoadjuvant) to shrink a large tumor and ease resection, or after surgery (adjuvant) to eliminate any remaining microscopic cancer cells. Adjuvant radiation is generally recommended for high-grade tumors, those larger than five centimeters, or when surgical margins were not clear of cancer cells.
Chemotherapy has a limited role, as MPNSTs are often resistant to these drugs. It is typically reserved for cases of metastatic disease or for tumors that are unresectable due to their location or size. The regimens used are similar to those for other soft tissue sarcomas, often involving anthracycline-based agents like doxorubicin.