Chemotherapy-Induced Peripheral Neuropathy
Chemotherapy-induced peripheral neuropathy (CIPN) is nerve damage caused by certain cancer treatments. It most often affects the peripheral nerves in the hands and feet, which is why symptoms commonly begin in a “glove and stocking” pattern. Patients may experience numbness, tingling, burning pain, heightened sensitivity to touch or cold, weakness, or trouble with balance and fine motor tasks. CIPN can progress to become severe enough to interfere with walking, daily activities, and sleep. These symptoms can sometimes force dose reduction or early discontinuation of chemotherapy. Not all chemotherapy drugs carry the same risk. CIPN is especially associated with agents such as taxanes, platinum drugs, vinca alkaloids, and bortezomib, though the pattern and severity of nerve injury differ by drug class. For some patients, symptoms improve after treatment ends, but for others they can persist for months or years. That is one reason CIPN matters so much clinically: it is not just a temporary side effect, but sometimes a long-term neurological complication of otherwise life-saving therapy. Unlike other neurodegenerative diseases, its cause is entirely induced by drugs meant to kill cancer. It is best understood as treatment-related nerve injury, often centered on damage to long sensory axons, though other cell types and pathways can contribute depending on the chemotherapy involved.
Pathology
The most important biological feature in many forms of CIPN is axon degeneration, especially in long sensory nerves. Axons are the long extensions of neurons that carry signals over distance. Because the nerves reaching the toes and fingers are especially long, they are often the most vulnerable when chemotherapy disrupts the cell’s ability to maintain them. This helps explain why symptoms usually start distally and then move upward if the injury worsens. Different drugs injure the peripheral nervous system in different ways. Some disrupt microtubules, which are part of the cell’s internal transport system and are especially important in axons. Others damage DNA, alter ion channel function, injure mitochondria, or trigger inflammatory responses in nerve tissue. Even when the upstream trigger differs, many of these insults converge on a common problem: the axon becomes metabolically stressed and begins to degenerate. There is also growing interest in the distinction between axon injury and neuron death. In classic CIPN, the dominant problem is often axons remaining in a sick but viable state instead of the neuron dying. That distinction matters because axon degeneration may be more preventable or reversible if the right pathways are blocked early enough.
Biological Pathways
One major pathway in CIPN is mitochondrial dysfunction. Peripheral axons have high energy demands, and several neurotoxic chemotherapies impair mitochondrial function, increase reactive oxygen species, and disrupt the energy balance needed to keep long axons healthy. Once that metabolic support begins to fail, the axon becomes increasingly fragile. Another major pathway is impaired axonal transport. Because a single neuron can stretch multiple feet from the spinal cord to the fingertips, axons depend on continuous transport of proteins, organelles, and signaling molecules from the body of the cell throughout the axon. Chemotherapies that interfere with microtubules can disrupt this transport system, increasing the stress at the far ends of the nerves. A third important pathway is the regulated self-destruction program controlled by SARM1. SARM1 is now understood as a central executioner of pathological axon degeneration. In preclinical models of CIPN, including paclitaxel- and cisplatin-related injury, SARM1 activity has been strongly linked to axon loss, and removing or inhibiting this pathway can be protective. This has made SARM1 one of the most compelling mechanistic targets in the field. There is also emerging evidence that SARM1 may intersect with PARP-linked cell death biology in some contexts. A 2025 study from Tong Wu and colleagues proposed that SARM1 is an essential component of neuronal parthanatos, a form of cell death connected to hyperactive PARP1 signaling after DNA damage. This work is broader than CIPN specifically, and it is yet to be validated clinically, but it is relevant because DNA-damaging stress and NAD+ depletion may help connect axon degeneration and neuronal injury more tightly than previously appreciated.
Progression
CIPN often begins during chemotherapy, but the exact timing depends on the drug. Symptoms may start gradually and worsen as the cumulative dose rises. In some patients, neuropathy continues to worsen for a period even after treatment stops, a phenomenon sometimes called “coasting,” especially with certain platinum agents. The course after chemotherapy is variable. Some patients improve meaningfully over time, especially if the injury was recognized early and treatment was adjusted. Others are left with chronic numbness, pain, or gait instability that can persist long after their cancer therapy is finished. This lingering burden is one reason CIPN has become such a major survivorship issue in oncology. Progression also reflects the underlying biology: once an axon degenerates beyond a certain point, recovery is slow and may be incomplete. That is why prevention and early intervention are so important.
Causes
The direct cause of CIPN is exposure to neurotoxic chemotherapy, but risk is not the same for every patient. Important factors include the specific drug, cumulative dose, treatment duration, and whether neurotoxic agents are combined. In other words, the treatment itself is the main driver, but the details of that treatment matter a great deal. Patient-level susceptibility also varies. Preexisting neuropathy, diabetes, older age, and other medical comorbidities may increase risk in some settings, although the strength of these associations can vary across studies and drug classes. This is one reason CIPN is often discussed as a multifactorial complication rather than a completely predictable toxicity. Researchers are also looking at whether genetic background influences who develops severe neuropathy, but this remains an evolving area. At present, there is still no universally accepted biomarker or genetic test that can reliably predict which patients will develop clinically significant CIPN before treatment starts.
Treatment Landscape
At present, the treatment landscape for CIPN is still limited. The most effective strategy remains prevention through dose adjustment, regimen selection when possible, and early recognition of symptoms during chemotherapy. Once neuropathy develops, treatment is largely focused on symptom management rather than repairing the damaged nerve. For painful CIPN, medications such as duloxetine have the strongest guideline-level support, though benefit is often partial rather than dramatic. Other commonly used pain medications may help some patients, but no widely accepted therapy reliably reverses the underlying nerve injury. Physical therapy, balance training, and practical safety measures are often important for preserving mobility and reducing fall risk. What is exciting is that the field is moving toward mechanism-based neuroprotection. Because axon degeneration is such a central feature of CIPN, therapies that prevent axons from entering a self-destruction program could be much more effective than simply treating pain after the damage is already done. That is one reason SARM1 has become such a prominent target in preclinical drug development.
Research Directions
One major research direction is finding better ways to predict who is at highest risk before symptoms become severe. This includes biomarker work, improved clinical phenotyping, and better animal and cellular models that capture the differences among taxanes, platinum drugs, and other chemotherapy classes. Another major direction is direct targeting of axon degeneration pathways. SARM1 inhibition has become especially interesting because multiple preclinical studies suggest that blocking SARM1 can protect axons from chemotherapy-related injury. That does not yet mean a clinically proven therapy exists, but it is one of the clearest examples of a target that matches the core biology of the disease. Researchers are also exploring how mitochondrial stress, calcium dysregulation, inflammation, and DNA damage responses interact. The newer PARP-SARM1 work adds to this by suggesting that SARM1 may sit at an important crossroads between axon degeneration and broader neuronal death pathways.