Peripheral numbness and tingling sensations are often symptoms of peripheral neuropathy, a condition involving damage to the nerves outside the brain and spinal cord. Cancer can indeed cause this numbness, not through a single mechanism, but through a variety of complex pathways involving the tumor’s physical presence, the body’s systemic response to the disease, and the side effects of necessary treatments. Understanding these distinct causes is fundamental to identifying the source of the sensation and managing the symptoms effectively.
When Cancer Directly Affects Nerves
The physical growth of a tumor mass can directly injure or compress nearby nerve structures, leading to numbness or weakness in the affected area. This is a mechanical cause where the expanding cancer physically interferes with the nerve’s ability to transmit signals. The location of the tumor dictates the pattern of numbness, often resulting in a localized rather than widespread effect.
Cancers that develop near major nerve bundles or in confined spaces are likely to cause these symptoms. For example, a tumor in the upper part of the lung, known as a Pancoast tumor, can press upon the brachial plexus. This compression often results in numbness and tingling along the inner arm and fingers. Similarly, cancers that spread to the spinal column can cause metastatic spinal cord compression. This is considered a medical emergency and can cause numbness, pins and needles, and weakness in the limbs and torso, depending on the level of the spine affected.
The tumor cells can also directly invade the nerve tissue itself, destroying the nerve fibers and disrupting signal transmission. When this invasion occurs, it can cause pain in addition to the loss of sensation and motor function. In these instances, the numbness is a direct result of the structural destruction of the neural pathway by the cancer cells.
Systemic Effects that Trigger Numbness
Numbness can arise from cancer even when the tumor is not physically touching a nerve, through indirect, systemic processes that affect nerve health throughout the body. One such indirect cause is a paraneoplastic syndrome, a rare complication where the body’s immune response to the cancer mistakenly attacks healthy nerve cells. The cancer cells produce antigens that the immune system recognizes, but these antigens are structurally similar to proteins found on nerve tissue. This immune cross-reaction leads to the production of autoantibodies that attack the nervous system, causing sensory neuronopathy, which results in numbness and loss of sensation. Paraneoplastic syndromes are most frequently associated with small-cell lung cancer, breast, ovarian cancer, and lymphoma, and the neurological symptoms can sometimes appear before the cancer is even diagnosed.
The cancer burden can also disrupt the body’s metabolism and nutritional balance, which are necessary for maintaining nerve health. Prolonged illness or cancer-related gastrointestinal issues can lead to deficiencies in essential vitamins like B1, B6, B12, Vitamin E, and copper. Since these nutrients are vital for nerve function and repair, their depletion can cause a generalized polyneuropathy, manifesting as bilateral numbness in the extremities. Certain blood cancers, such as multiple myeloma, can also produce abnormal proteins that directly deposit in or damage the peripheral nerves, triggering numbness and pain in the legs.
Numbness Caused by Cancer Treatments
Treatment-induced nerve damage, known as chemotherapy-induced peripheral neuropathy (CIPN), is a frequent cause of numbness experienced by cancer patients. The prevalence of CIPN is high, with up to 85% of patients treated with certain neurotoxic agents experiencing some degree of neuropathy.
Platinum-based drugs, such as cisplatin and oxaliplatin, damage nerve cells primarily by interfering with mitochondrial function and causing oxidative stress within the sensory neurons. Oxaliplatin is also known for causing an acute, transient form of neuropathy that is often triggered or worsened by exposure to cold temperatures. Taxanes, including paclitaxel and docetaxel, cause nerve damage by disrupting the microtubules, which are the internal structural components essential for transporting materials within the long axons of nerve cells.
Vinca alkaloids, such as vincristine, also disrupt these microtubule structures, impairing axonal transport and leading to nerve dysfunction and numbness. This damage is often dose-dependent and cumulative, meaning the severity of numbness tends to increase with the total amount of drug received over time.
In addition to chemotherapy, radiation therapy can also cause nerve damage, known as radiation plexopathy, when high doses are delivered near major nerve plexuses, such as the brachial or lumbosacral plexus. This form of injury is characterized by a delayed onset, often developing months or even years after the completion of the radiation treatment, due to progressive nerve compression from scar tissue formation and microvascular damage.
Identifying Symptoms and Medical Evaluation
The numbness associated with cancer-related neuropathy typically presents as a “glove-and-stocking” pattern, affecting the hands and feet symmetrically. Patients often describe the sensation as pins and needles, burning, prickling, or a complete loss of feeling, making it difficult to perform fine motor skills like buttoning a shirt or maintaining balance. Any new or worsening numbness must be reported promptly to the medical team, as it may necessitate a change in treatment or signal a serious complication like spinal cord compression.
Medical evaluation begins with a detailed neurological exam to test reflexes, muscle strength, and sensory perception. Blood tests are frequently used to check for underlying metabolic contributors, such as vitamin B12 deficiency or abnormal protein levels associated with certain blood cancers.
To assess the extent of nerve damage, specialized tests like Nerve Conduction Studies (NCS) and Electromyography (EMG) are employed. NCS measures how quickly electrical signals travel through the nerves. EMG assesses the electrical activity of the muscles, helping determine if the problem lies in the nerve axon or the surrounding myelin sheath. Imaging studies, such as Magnetic Resonance Imaging (MRI), are also used to rule out tumor compression or invasion as the direct cause of the symptoms.