Peripheral neuropathy, the medical term for numbness, tingling, and altered sensation, is a recognized symptom that can be directly or indirectly linked to a cancer diagnosis. This condition results from damage to the peripheral nerves, which transmit signals between the central nervous system—the brain and spinal cord—and the rest of the body. Numbness in a patient with cancer does not have a single cause, but rather it stems from several distinct mechanisms related to the disease’s activity or the necessary treatments used to fight it. The resulting sensory changes can significantly impact a patient’s quality of life and may affect the hands, feet, or other specific areas of the body.
Numbness Caused by Direct Tumor Pressure
One straightforward way cancer causes numbness is through physical obstruction, where a growing tumor mass physically compresses or invades nearby nerve tissue. As the tumor expands, it exerts pressure on the peripheral nerves, nerve roots, or even the spinal cord, which disrupts the normal transmission of electrical signals. This mechanical interference leads to sensory changes, often described as numbness, tingling, or pain, in the area of the body supplied by the affected nerve.
A tumor located in the apex of the lung, known as a Pancoast tumor, can compress the bundle of nerves called the brachial plexus, leading to numbness, weakness, and pain in the shoulder and arm. Similarly, tumors in the pelvis or abdomen may press upon the lumbosacral plexus, causing symptoms in the legs and feet. In aggressive cancers, the malignant cells do not just push against the nerve, but actually infiltrate and destroy the nerve tissue itself, which causes a destructive neuropathy. Metastatic cancer that spreads to the spine can also press on the spinal cord, resulting in numbness and coordination issues that can affect both sides of the body.
Systemic Causes Related to Cancer Activity
Numbness can also arise from systemic effects of cancer that do not involve direct physical contact between the tumor and the nerve. The body’s immune response to the cancer can trigger a condition called a paraneoplastic syndrome, where the immune system mistakenly attacks healthy nerve cells. This happens because the cancer cells produce substances, known as onconeural antigens, that are similar to proteins found on nerve tissue. The antibodies generated to attack these antigens then cross-react with the nervous system, causing damage and resulting in numbness and other neurological symptoms.
Paraneoplastic syndromes often manifest as a sensory neuronopathy, which primarily destroys the sensory neurons located in the dorsal root ganglia. This type of nerve damage can produce severe sensory symptoms, including numbness, and can sometimes appear months or even years before the underlying cancer is formally diagnosed. Small-cell lung cancer is frequently associated with these syndromes, often linked to the presence of specific antibodies like anti-Hu. Beyond immune reactions, some cancers can also cause metabolic imbalances, such as severe nutritional deficiencies or abnormal calcium levels, which can disrupt the delicate environment required for proper nerve function.
Neuropathy Caused by Cancer Treatment
The most frequent cause of numbness in cancer patients is damage resulting from chemotherapy, a condition referred to as Chemotherapy-Induced Peripheral Neuropathy (CIPN). Certain classes of chemotherapy drugs are neurotoxic, meaning they directly damage the peripheral nerves, leading to symptoms like tingling, pain, and numbness, typically in a “stocking-and-glove” pattern affecting the hands and feet first. Platinum-based agents, such as cisplatin and oxaliplatin, are well-known neurotoxic drugs that can cause CIPN by altering voltage-dependent sodium channels and inducing oxidative stress in the axons.
Taxanes (paclitaxel and docetaxel) and vinca alkaloids (vincristine) are other major classes of drugs that frequently cause nerve damage. The severity of CIPN is often dose-dependent, meaning symptoms worsen with higher cumulative doses of the medication, sometimes forcing a reduction in treatment to prevent irreversible damage. Some neurotoxic effects, like the acute cold sensitivity associated with oxaliplatin, can appear immediately, while others develop gradually over the course of treatment.
Nerve damage can also occur due to other cancer treatments, including radiation therapy and surgery. Radiation delivered to areas like the chest, neck, or armpit can cause a delayed injury to the brachial plexus, leading to numbness and weakness that may not appear until months or years after the treatment ends. Surgical removal of a tumor or nearby lymph nodes can inadvertently sever, stretch, or otherwise injure surrounding nerves, resulting in immediate numbness or chronic nerve pain in the surgical site. For example, breast cancer surgery may cause persistent numbness or tingling in the arm.
Diagnosis and Management of Symptoms
Accurately diagnosing the cause of numbness begins with a thorough physical and neurological examination to assess the distribution and severity of sensory loss and weakness. Diagnostic imaging, such as magnetic resonance imaging (MRI) or computed tomography (CT) scans, is often used to determine if a tumor is directly pressing on a nerve or the spinal cord. Specialized tests, including nerve conduction studies and electromyography (EMG), can help measure the extent of nerve damage and distinguish between nerve compression and damage to the nerve cell body.
Management focuses on alleviating symptoms, as there are limited options to reverse existing nerve damage. Pharmaceutical interventions for nerve pain and numbness often include medications initially developed for other conditions, such as the anticonvulsants gabapentin and pregabalin. Certain antidepressants, specifically duloxetine, have also shown effectiveness in reducing the pain associated with CIPN.
Non-pharmaceutical approaches are also important for managing functional limitations and include physical and occupational therapy. Therapists can help patients with strength training, balance exercises, and the use of assistive devices to maintain mobility and reduce the risk of falls. Patients are encouraged to immediately report any new or worsening symptoms of numbness to their care team, as early detection can sometimes allow for adjustments to treatment that minimize further nerve damage.