Red light therapy and
cancer treatment

The distinction that changes everything

Cancer treatment works. Chemotherapy, radiotherapy, and haematopoietic stem cell transplantation now save and extend lives that would have been lost a generation ago. But the collateral damage they cause to healthy tissue is severe, and for many patients it is the side effects - not the disease - that determine whether treatment can continue at full dose or has to be reduced or stopped. Oral mucositis severe enough to prevent eating. Radiation burns across the chest or neck. Peripheral neuropathy that persists for years after chemotherapy ends. These are not minor inconveniences.

This is where photobiomodulation - red and near-infrared light therapy - has one of its best-evidenced and most clinically recognised roles. The question of whether red light therapy affects cancer cells or cancer progression is not yet resolved, and we will not pretend otherwise. But the question of whether it helps manage certain side effects of cancer treatment is far better answered. The evidence is substantial, some of it guideline-level, and it is backed by dozens of randomised controlled trials across multiple independent research groups.

The distinction between those two questions matters enormously. This blog is about the second one.

Where the evidence sits

The applications covered in this blog fall into three distinct tiers based on the quality and quantity of clinical evidence behind them.

Oral mucositis is the most common acute complication of cancer treatment. It starts with redness and swelling of the mouth lining - typically appearing 3 to 7 days into a chemotherapy cycle or over the course of radiotherapy - and progresses through increasingly painful ulcers that can make eating, swallowing, and speaking impossible. At its most severe, it requires hospitalisation, parenteral nutrition, and opioid pain management. It also forces dose reductions and treatment interruptions that can compromise the oncological outcome.

Between 20% and 40% of patients receiving conventional chemotherapy develop oral mucositis - rising to 80% or more with high-dose regimens before stem cell transplantation. Among those having head and neck radiotherapy, nearly all patients are affected. And despite decades of research, the standard arsenal against it - oral hygiene protocols, topical agents, analgesics - remains only partially effective.

PBM is the exception. The Multinational Association of Supportive Care in Cancer and the International Society of Oral Oncology (MASCC/ISOO) published formal clinical practice guidelines recommending PBM for the prevention of oral mucositis and its associated pain across three distinct treatment settings: haematopoietic stem cell transplantation, head and neck radiotherapy without chemotherapy, and head and neck radiotherapy combined with chemotherapy. For each setting, the guidelines specify one or two validated treatment protocols with exact parameters - wavelength, energy density, application frequency - that clinicians are advised to follow precisely.

The 2024 meta-analysis by Shen et al. in Head and Neck examined RCTs specifically in head and neck cancer patients receiving chemoradiotherapy, finding that PBM significantly reduced the incidence and severity of oral mucositis: relative risk of 0.49 for severe mucositis in treated patients versus controls. A separate 2025 systematic review (Biomedicines, 13(2):268) confirmed the effectiveness of preventive PBM protocols across chemotherapy-only patients, with no significant adverse effects reported across the reviewed trials.

Radiation dermatitis affects around 95% of patients receiving radiotherapy. The skin within and around the treatment field breaks down in response to cumulative radiation dose, moving through redness and dryness in the early stages to moist desquamation - open, weeping skin - in severe cases. For breast cancer patients receiving chest wall irradiation, or head and neck patients, the affected areas are large, the pain is significant, and the skin breakdown can necessitate treatment breaks that compromise tumour control.

PBM addresses radiation dermatitis through the same wound healing and anti-inflammatory mechanisms documented in the wound healing blog. Radiation damages skin cells by generating reactive oxygen species and impairing mitochondrial function - creating the same metabolically stressed cellular environment in which PBM's effects are most pronounced. Applied to the skin surface before or during the radiotherapy course, PBM supports cellular repair and reduces the severity of the inflammatory cascade that drives progressive skin breakdown.

A 2025 meta-analysis published in Radiotherapy and Oncology (Lin et al., PMID 39426526) reviewed 8 studies (5 RCTs and 3 non-RCTs). Compared to standard care, PBM-treated patients had significantly lower incidence of grades 2 and 3 radiation dermatitis: risk difference of -0.36 (95% CI -0.53 to -0.19, p less than 0.00001). The LABRA trial (breast cancer patients) and DERMISHEAD trial (head and neck cancer patients), both using LED-based PBM, contributed to this picture with consistent findings across independent research groups. The 2025 JAAD expert consensus - 21 specialists, systematic literature review, Delphi process - lists acute radiation dermatitis as one of PBM's established clinical applications.

Chemotherapy-induced peripheral neuropathy is one of the most under-recognised long-term problems in cancer survivorship. Drugs including taxanes, platinum compounds, and vinca alkaloids damage peripheral nerves, causing numbness, tingling, burning pain, and loss of sensation most commonly in the hands and feet. For around 30% of patients it persists for years after treatment ends. It affects balance, grip, the ability to feel heat or cold, and quality of daily life in ways that are invisible from the outside but profoundly limiting in practice.

The mechanism connecting PBM to peripheral nerve function is the same one that underpins its effects in diabetic neuropathy: nerve cells have exceptionally high energy demands, and when their mitochondrial function is disrupted - as it is by chemotherapy - their ability to maintain signal transmission and support their own repair deteriorates. PBM's stimulation of cytochrome c oxidase directly addresses mitochondrial dysfunction, and NIR wavelengths (810-850nm) penetrate deeply enough to reach peripheral nerve tissue in the hands and feet.

The NEUROLASER trial (Lodewijckx et al. 2022, Support Care Cancer, PMID 35312857) randomised 32 breast cancer patients to PBM or placebo during chemotherapy. The PBM group had significantly better quality of life scores, less worsening of sensory neuropathy symptoms, and faster recovery of functional measures including six-minute walk distance and pain levels after chemotherapy completion. A 2024 systematic review in Frontiers in Oncology covering 23 oncology PBM studies confirmed that PBM mitigates peripheral neuropathy and improves quality of life in chemotherapy patients. The application is relevant both during active chemotherapy - where it may reduce how much neuropathy develops - and after treatment ends, where it may support gradual recovery of nerve function.

When radiotherapy is delivered to the head and neck - for cancers of the mouth, throat, larynx, or nasopharynx - the salivary glands are often caught in or near the treatment field. The resulting damage reduces saliva production, sometimes permanently. Xerostomia causes difficulties with eating, swallowing, and speaking. It contributes to dental decay, oral infections, and disrupted sleep. For many patients who are otherwise cured of their cancer, it remains a daily limitation for years or decades.

PBM has been investigated for xerostomia on the same biological basis as its oral mucositis evidence: the oral cavity is directly accessible to light, the affected tissue is exactly the compromised, energy-depleted cellular environment in which PBM is most effective, and the inflammation and mitochondrial disruption driving salivary gland dysfunction are the same targets PBM addresses in other contexts. Clinical studies including RCTs in head and neck cancer patients post-radiotherapy have shown improvements in salivary flow rates and patient-reported dry mouth severity with consistent PBM treatment. The MASCC/ISOO Clinical Practice Statement on salivary gland hypofunction, published in Supportive Care in Cancer in 2024, reviewed the available evidence and included PBM among the modalities with supporting data in this setting.

Cancer-related fatigue is the most commonly reported symptom across all cancer types and treatment modalities. It is distinct from ordinary tiredness in that it does not resolve with rest, it persists through and beyond treatment, and it can be severe enough to prevent work, socialising, and basic daily activity. The mechanism is complex and multifactorial - inflammation, mitochondrial dysfunction, hypothalamic-pituitary-adrenal dysregulation, anaemia - but the mitochondrial component is significant and directly maps to what PBM targets.

The evidence here is earlier stage than for mucositis or radiation dermatitis. Several pilot trials and observational studies have reported improvements in fatigue scores and quality of life measures in cancer patients receiving concurrent PBM, but we are not yet at the level of large, well-powered RCTs confirming this effect definitively. The biology is plausible and consistent with PBM's established mechanisms. Larger trials are currently running. This is worth watching, but should not be cited with the same confidence as the applications above.

The safety question - what we know and what we do not

One question comes up constantly when people going through cancer treatment consider PBM: could it stimulate cancer cell growth? It is a fair question and deserves a direct answer rather than being brushed aside.

The honest answer is that this is not fully resolved in the scientific literature - and anyone who tells you otherwise in either direction is overstating the evidence. What we do have is a substantial body of clinical data from patients undergoing cancer treatment concurrently with PBM, and across those human studies the consistent finding is no increase in tumour growth or recurrence. A comprehensive 2020 review by Sperandio et al. covering human trials, animal studies, and in vitro work concluded that "PBM should be considered as part of the standard of care for specific oncology purposes" and that "the safety of PBM concerning the effect on the tumour response and most importantly the benefit of PBM to patients in the management of cancer treatment-related toxicities have been shown in in vivo studies and clinical trials." The same review, however, was clear that "vigilance remains warranted for applications that have not been adequately documented or without guidelines due to a lack of evidence."

The picture in animal studies is more mixed than the human data. Roughly half of animal studies show inhibited or neutral tumour growth with PBM, and some show promotion. In vitro (cell culture) studies are even more contradictory - some suggest PBM may favour tumour progression in oral squamous cell carcinoma cells via the Akt/mTOR pathway, while others report a reduction in tumour growth. As the review notes, in vitro results have limited applicability compared to in vivo studies where multiple physiological systems interact. The conditions under which promotion has been observed in vitro differ significantly from standard clinical parameters.

One important limitation of the human evidence base is its short follow-up. Most human studies use only one to three PBM sessions, which means we do not yet have long-term data on repeated use in cancer patients over months or years. This is not evidence of harm - it is a gap. The 5-year oncological outcomes data that does exist from PBM supportive care registries shows no adverse signal, but this needs to be stated clearly rather than assumed.

What the World Association for Laser Therapy (WALT) advises - and this is a firm position, not a suggestion - is that panels should not be used directly over a known tumour site. That guidance holds without exception.

For anyone who wants to read further into the full evidence base on PBM and oncology safety, researcher Vladimir Heiskanen maintains a publicly available database of over 200 studies on light therapy and oncology, covering human trials, animal studies, and in vitro work across different cancer types and treatment parameters.

Why this matters

Cancer treatment has become increasingly effective at extending and saving lives. But survivorship - the quality of life during and after treatment - has not always kept pace. Oral mucositis severe enough to require opioid pain management and hospitalisation. Radiation burns that force treatment breaks. Neuropathy that persists for years after the last chemotherapy infusion. These problems are real and they affect enormous numbers of people.

PBM does not change the oncological outcome. It does not cure or prevent cancer. What the evidence supports is that it can meaningfully reduce the severity of certain side effects that make treatment harder to get through and recovery harder to complete. For oral mucositis specifically, it has formal guideline backing from the leading international body in supportive oncology care. For radiation dermatitis, the 2025 expert consensus places it in the established category. For CIPN, the trial evidence is building toward the same conclusion.

For someone facing months of chemotherapy or a course of head and neck radiotherapy, a genuine reduction in the severity of mucositis or skin breakdown is not a small thing. It can mean the difference between completing treatment at full dose and having it reduced or interrupted. That is where the evidence sits, and it is where we have tried to keep this blog.