TL;DR: The fear that hyperbaric oxygen therapy (HBOT) might “feed” cancer comes from a real piece of biology, but it conflates that with how HBOT actually works in the human body. Major hyperbaric medicine bodies (UHMS, ECHM) and the published cohort literature have found no signal that HBOT promotes cancer recurrence in survivors treated for radiation injury. Active malignancy in the planned treatment field is a relative contraindication and warrants individual judgment, but a remote history of cancer is not a barrier to HBOT in Canada. Daffodil Month is a fitting moment to address the question honestly: this post walks through the biology, the evidence, and what Canadian cancer centres actually do in practice.

Hyperbaric oxygen therapy (HBOT) is a medical treatment in which a patient breathes 100 percent oxygen at elevated atmospheric pressure inside a sealed chamber. Each session typically runs 90 minutes at 2.0 to 2.4 atmospheres absolute, delivered five days a week for a treatment course of 20 to 60 sessions. In Canada, HBOT is publicly funded for 14 Health Canada-recognised conditions, including delayed radiation injury, radiation cystitis, and osteoradionecrosis of the jaw. All three of those are common reasons that cancer survivors are referred to hyperbaric programmes.

April is Daffodil Month in Canada, the Canadian Cancer Society’s flagship awareness and fundraising drive. Through this series, Canada Hyperbarics has been answering the questions cancer survivors actually ask about hyperbaric oxygen therapy. Few questions come up more often than this one: “If oxygen feeds cells, doesn’t HBOT feed the cancer too?” It is a fair, intuitive question. Let’s give it a fair, evidence-based answer.

Where does this concern come from?

The concern is rooted in a real observation from cancer biology. Solid tumours grow faster than their blood supply can keep up with, so the centres of many tumours become severely hypoxic, meaning starved of oxygen. Cancer cells in these hypoxic regions adopt a metabolism that helps them survive the low-oxygen environment, and they become substantially more resistant to radiation therapy and several chemotherapies. From a distance, the logic looks simple: low oxygen helps tumour cells, so high oxygen must do the opposite and feed them.

Reinforcing the worry is the in-vitro evidence: when you culture tumour cell lines in petri dishes under high oxygen, they often grow vigorously. That observation has shown up in many laboratory papers and is sometimes cited as proof that HBOT must be unsafe for cancer survivors. The leap from “tumour cells like oxygen in a dish” to “HBOT will make my cancer come back” feels like common sense, but the biology between those two statements is not what the leap implies.

Why is the biology more complicated than the myth?

Three details change the picture once you look closely.

Aspect Petri-dish observation Real-world clinical reality
Oxygen exposure Continuous, perfectly diffused Intermittent (90 min/day, 5 days/week)
Tumour environment Single-cell-line monoculture, no blood supply, no immune system Complex tumour bed with blood supply, immune surveillance, regulatory signals
Effect on radiation therapy Not directly studied Better oxygenation makes radiation more effective at killing tumour cells
Cohort recurrence signal N/A (no patients) No signal in published cohort studies of cancer survivors who received HBOT

HBOT is intermittent, not chronic. A typical hyperbaric treatment course is 20 to 40 sessions over four to eight weeks, with each session lasting 90 minutes. The remaining 23 hours each day, your tissues sit at normal oxygen levels. Tumour cell growth in a petri dish under continuous high oxygen has very little in common with a person who breathes oxygen at pressure for 90 minutes every weekday and then returns to ordinary breathing for the rest of their life.

HBOT can actually make tumours more radiation-sensitive, not less. The hypoxic tumour core that resists radiation is precisely the region HBOT briefly oxygenates. This was the original rationale that led Japanese radiation oncologists, beginning in the 1980s, to test HBOT immediately before each radiotherapy fraction in glioblastoma. The hypothesis is that better oxygenation makes the radiation dose more effective at killing tumour cells. The evidence base is preliminary and the protocol is logistically demanding, but the underlying idea is the opposite of “feeding the tumour”: it is using oxygen to make the cancer treatment hit harder.

Petri-dish biology does not translate cleanly into human bodies. Tumour cells in a flask are surrounded by a perfectly diffused medium with no immune system, no blood supply, no neighbouring tissue, and no time-of-exposure constraint. Real tumours in real people exist within an immune environment, are limited by blood supply, and are subject to the body’s complex regulatory systems. Reducing what happens in a dish to a prediction about a human course of HBOT misses most of the relevant biology.

What does the real-world evidence actually show?

The most relevant question is not what tumour cells do in a dish but what happens to cancer survivors who receive HBOT in clinical practice. Here the evidence is increasingly clear.

The Undersea and Hyperbaric Medical Society (UHMS), the international scientific society for hyperbaric medicine, has reviewed this question across multiple editions of its Hyperbaric Oxygen Therapy Indications handbook. The current 15th edition (2024) and the longer-standing UHMS position statement on cancer both conclude there is no evidence that HBOT promotes cancer growth or recurrence. Several large registry studies and cohort series tracking irradiated cancer survivors who received HBOT for late radiation injury have failed to detect a recurrence signal. The 2016 Cochrane Review on hyperbaric oxygen therapy for late radiation tissue injury, which pooled data from 14 randomised trials and 753 participants and was updated in 2020, similarly found no harm signal.

Real-world cohorts in Canada tell the same story. The Princess Margaret Cancer Centre in Toronto is among the leading Canadian academic centres integrating HBOT into post-cancer care, particularly for brain radiation necrosis after radiotherapy for primary or metastatic tumours. Major Canadian hospital hyperbaric programmes (Toronto General, Hamilton General, The Ottawa Hospital, Vancouver General, Misericordia Edmonton, Foothills Calgary) treat cancer survivors with delayed radiation injury as part of routine practice. Delayed radiation injury is one of the 14 Health Canada-recognised conditions for which provincial health insurance covers HBOT, and the patients receiving it are by definition cancer survivors. The fact that this is publicly funded and standard care across the country reflects a clinical and regulatory consensus, not an oversight.

What are the real contraindications?

The honest answer to “what should make me cautious about HBOT?” is not “the risk of cancer recurrence.” It is a short list of specific clinical situations that hyperbaric medicine programmes screen for at intake.

Active recurrent malignancy in the planned treatment field is a relative contraindication for elective HBOT (most commonly when planning treatment for delayed radiation injury). This is not because HBOT has been shown to fuel growth (it has not), but because most Canadian programmes prefer to confirm the diagnosis is necrosis (or another HBOT-treatable late effect) and not active disease before committing the patient to a long course of treatment. Where the diagnostic distinction is unclear (radiation necrosis can mimic recurrence on imaging), biopsy and multidisciplinary tumour-board review are standard pre-treatment work-up. A remote history of cancer with no current evidence of disease is not a contraindication.

Bleomycin chemotherapy is an absolute contraindication, but the reason has nothing to do with cancer growth. Bleomycin is associated with oxygen-induced pulmonary fibrosis, and patients who have received bleomycin can develop severe lung injury when exposed to high oxygen pressures, even years after the chemotherapy ended. The contraindication is about lung safety, not about cancer.

Disulfiram, used for alcohol-use disorder, interferes with antioxidant defences and is also contraindicated. Again, the issue is metabolic safety, not cancer.

None of the standard hyperbaric contraindications are about cancer growth. The screening process is designed to keep patients safe from oxygen-related complications, not to filter out cancer survivors.

What do Canadian cancer centres actually do?

If HBOT genuinely posed a recurrence risk for cancer survivors, the major Canadian cancer centres and hyperbaric programmes would not be sending patients into chambers as a routine part of post-cancer care. They are. Treatment for delayed radiation injury, including osteoradionecrosis of the mandible, osteoradionecrosis of the ribs after thoracic radiation, radiation cystitis after pelvic radiation for prostate or cervical or bladder cancer, radiation proctitis, soft-tissue radionecrosis, and brain radiation necrosis, is one of the most-referred non-emergency hyperbaric indications in Canada. The patients receiving it are cancer survivors by definition, and the evidence base supporting their treatment is among the strongest in hyperbaric medicine.

The Marx 30-and-10 protocol, which delivers 30 HBOT sessions before planned dental surgery in an irradiated jaw and 10 more sessions afterward, has been the standard of care for prevention of mandibular osteoradionecrosis since the 1980s. It is offered to head-and-neck cancer survivors at hospital programmes across the country. The 2019 RICH-ART trial published in Lancet Oncology and its 2025 five-year follow-up in EClinicalMedicine demonstrate sustained benefit of HBOT for radiation cystitis in pelvic-cancer survivors with no recurrence signal. The Canada Hyperbarics research database of more than 14,000 peer-reviewed HBOT studies includes the full literature on cancer-survivor outcomes for anyone who wants to read further.

How should I talk to my oncologist?

If you are a cancer survivor considering HBOT for a delayed radiation complication or another approved indication, the right path is a conversation with your oncology team and a referral to a hospital hyperbaric medicine programme. The hyperbaric medicine physicians work alongside oncology, radiation oncology, and surgical specialties, and they will review your specific cancer history, treatment timing, current scans, and any active concerns before recommending a course. Honest discussion is the standard of care; nobody is going to push you into the chamber without addressing your questions about safety.

Daffodil Month is a moment to bring questions like this into the open. The myth that HBOT might wake up dormant cancer is genuinely common, and it discourages cancer survivors from accessing a treatment that could meaningfully help with the late radiation effects they are quietly suffering through. The evidence does not support the myth. The Canadian cancer-care system, the international hyperbaric medicine community, and the published literature converge on the same answer: a remote history of cancer is not a barrier to HBOT, and for many cancer survivors with delayed radiation injury, HBOT is one of the most evidence-based treatments available to them.

Frequently asked questions

Will HBOT make my cancer come back? No clinical evidence supports this concern. Multiple cohort studies, the UHMS position statement, and the Cochrane Review of late radiation tissue injury have all found no recurrence signal in cancer survivors treated with HBOT. Active recurrent malignancy in the treatment field is a relative contraindication that warrants individual judgement, but a remote history of cancer is not a barrier to treatment.

If oxygen feeds tumour cells in a petri dish, why doesn’t it do the same in my body? Because the petri dish is a permanently oxygenated, immune-system-free, blood-supply-free environment that does not approximate human biology. HBOT in real patients is intermittent (90 minutes per session, daily), the body’s regulatory systems remain active, the tumour bed has its own complex microenvironment, and the integrated cohort evidence has not detected a harm signal. Laboratory observations are useful for generating hypotheses but are not predictive of clinical outcomes on their own.

What if I have an active cancer, not just a history of cancer? The decision is made by your oncology team in collaboration with the hyperbaric medicine programme. Active recurrent malignancy in the planned treatment field is a relative contraindication and most Canadian programmes prefer to confirm the diagnosis (with biopsy and multidisciplinary review) before committing to HBOT. There are situations (particularly investigational use of HBOT as a radiosensitiser before radiotherapy) where active cancer is the indication itself, but those are research-protocol cases at specific academic centres.

Are there any cancer treatments that are an absolute contraindication for HBOT? Bleomycin chemotherapy is the main one, and the reason is oxygen-induced lung fibrosis, not cancer growth. Patients who have received bleomycin should discuss the timing of any future HBOT with their oncology team. Most other chemotherapies are compatible with HBOT.

What HBOT indications are most relevant for Canadian cancer survivors? Late radiation injury is the dominant one. This includes osteoradionecrosis of the jaw or other bones, radiation cystitis, radiation proctitis, soft-tissue radionecrosis, and brain radiation necrosis. The Marx 30-and-10 protocol for dental work in irradiated jaws is also commonly offered prophylactically. All of these are publicly funded at hospital hyperbaric programmes under provincial health insurance.

Where can I find a Canadian hyperbaric programme that handles cancer-related referrals? The Canada Hyperbarics verified directory lists all 11 hospital programmes and 21 private clinics across nine provinces. The Princess Margaret Cancer Centre / UHN, Hamilton General, The Ottawa Hospital, Vancouver General, Misericordia Edmonton, and Foothills Calgary have particularly close working relationships with their associated cancer centres and are common destinations for radiation-injury referrals.

This Daffodil Month

If a friend or family member is a cancer survivor living with delayed radiation effects (chronic mouth pain after head and neck radiation, hematuria after pelvic radiation, ongoing pain in an irradiated bone or chest wall), the fear of “feeding the cancer” is one of the things that keeps them from raising HBOT with their oncology team. Sharing accurate information is one quiet way to help. The 2026 Daffodil Month campaign is at cancer.ca/daffodil, and a referral conversation with their cancer care team is the first step.

References

Disclaimer: This article is for informational purposes only and is not a substitute for individualised medical advice from your physician, oncologist, or hyperbaric medicine programme. The decision to pursue HBOT should be made in consultation with your cancer care team and a referring physician. Canada Hyperbarics is an independent educational project; we do not deliver hyperbaric treatment and do not have a financial relationship with any specific facility.