Cold atmospheric plasma, or CAP, is a room-temperature, ionized gas that can damage cancer cells while mostly sparing healthy cells. Scientists make CAP by adding energy to common gases. This creates reactive oxygen and nitrogen species, tiny bursts of UV light, and charged particles. Together, these cause strong stress inside tumor cells. Because the devices are small and the method does not require drugs, CAP is a flexible tool that can treat surface tumors on its own or be combined with surgery, chemotherapy, radiation, and immunotherapy.
How CAP Harms Tumors While Protecting Normal Tissue
Cancer cells already live with high stress from unstable chemistry inside the cell. CAP adds to that stress and pushes them past their limit. Several cell-death routes can switch on at once:
- Apoptosis: The cell’s power centers, the mitochondria, fail. Signals trigger caspases that break the cell down in an orderly way.
- Immunogenic cell death (ICD): Dying cells wave “danger” flags like calreticulin and release ATP and HMGB1. These call in dendritic cells and T cells that can attack the tumor.
- Pyroptosis: After damage, caspase-3 can cut gasdermin-E, which punches holes in the cell membrane. The cell swells and bursts, which alerts the immune system.
- Autophagy-dependent death: The cell tries to clean up damage, but if stress is too high, the cleanup process becomes self-destruction.
- Ferroptosis: Lipid fats in the cell membrane rust, in a sense, when glutathione and GPX4 defenses fall and iron fuels new radicals.
- Necrosis at high doses: Membranes rip, calcium floods in, and the cell contents spill out, which can further wake up immune defenses.
Which path dominates depends on the tumor’s genes and its local environment.
The Tools and the Gases
Most medical CAP systems are either DBD plates that treat a flat surface or plasma jets that blow a small, targeted plume. Argon and helium make smooth, steady plasma that is easy to control. Nitrogen and oxygen are cheaper and make more reactive species, but they need stronger power and can be less uniform.
Some devices are closer to the clinic. The kINPen argon jet is registered as a medical device in Europe. The Canady Helios™ helium system has U.S. clearance for soft-tissue ablation during surgery, and it has been used on surgical margins in early cancer studies.
Two Ways to Deliver CAP
Direct CAP touches the tumor or the surgical cavity with the plasma plume or field.
- In melanoma and breast cancer models, tumors grew more slowly. More dendritic cells and CD8⁺ T cells entered the tumor. After surgery, CAP applied to the cavity cut down on recurrences and extended survival.
- In glioblastoma models, a jet aimed over the skull slowed tumor growth. Adding temozolomide after CAP nearly stopped progression.
- In lung and head-and-neck models, CAP worked better with iron-oxide nanoparticles, cisplatin, or anti-PD-1 therapy. It also disrupted tumor energy use by blocking glycolysis and weakening AKT signals.
Indirect CAP carries CAP chemistry deeper or keeps it in place longer.
- CAP-activated liquids: Saline or culture media exposed to CAP hold reactive species. Doctors can inject or wash a cavity with them. In animal models of ovarian, lung, pancreatic, and colon cancers, these liquids shrank tumors, reduced spread, and sometimes triggered ferroptosis. They can also boost chemotherapy or work with special nanomaterials.
- Hydrogels: Thermosensitive or ROS-responsive gels store CAP species at the tumor site and release them slowly. Gels mixed with anti-PD-1 or TGF-β inhibitors reshaped the tumor environment, raised helpful immune cells, and sometimes shrank distant, untreated tumors, showing a body-wide immune effect.
- Long tubes and endoscopic probes: Thin, flexible tubes bring CAP into cavities or even the brain. Reactive species can fade with distance, so design and power settings matter.
- Microneedle patches: Hollow or cryo-frozen microneedles deliver CAP species through the skin with little pain. In melanoma models, hollow microneedles beat surface CAP, raised T-cell responses, and paired well with checkpoint drugs.
Each method has tradeoffs. Liquids are simple but dilute fast. Hydrogels keep CAP where you need it. Tubes and microneedles reach deeper spots but add engineering challenges.
What Animal Studies Show
Across many cancers, CAP:
- Slows or shrinks tumors through several death programs at once.
- Primes the immune system by triggering ICD, which improves antigen presentation and draws in CD4⁺ and CD8⁺ T cells.
- Combines well with chemotherapy, radiation, and checkpoint inhibitors, sometimes allowing lower drug doses.
- Helps after surgery by cleaning up the resection bed and lowering the risk of recurrence.
Results vary by cancer type, device, gas, dose, and schedule. Clear dosing rules and practical biomarkers will make results more consistent.
Early Signs in Patients
Early human work focuses on hard head-and-neck cases and on cleaning surgical margins:
- Germany, kINPen: Patients had less pain and odor from infected ulcerations and only mild side effects. Some showed partial tumor responses and better wound healing.
- USA and Israel, helium system during surgery: In 20 patients with stage IV or recurrent tumors, plasma applied to resection margins improved local control signals. Patients with complete resections did well, and those with microscopic positive margins did especially well. Safety looked acceptable. Larger controlled trials are the logical next step.
These results suggest CAP’s first clinical niche will be as an add-on to surgery to reduce local recurrence.
Why CAP Is Promising
- Local and drug-free: Ionized gas avoids many whole-body side effects and can be repeated.
- Multiple kill routes: Hitting many pathways at once can bypass common resistance.
- Immune boost: ICD and microenvironment changes help checkpoint therapy work better.
- Compact hardware: Devices are portable and easier to run than many other energy-based tools.
Where CAP Fits First
Watch for CAP in intra-operative margin treatment and post-resection cavity care to cut local recurrence. For non-resectable tumors, the best bets are:
- Combinations with checkpoint drugs to take advantage of ICD.
- Chemo-sensitization where extra oxidative stress helps DNA-targeting or mitochondrial drugs.
- Radiation synergy that layers on more oxidative damage.
Hydrogels, microneedles, and endoscopic micro-jets may bring these gains to deeper or hard-to-reach tumors.
The field is shifting from proof-of-concept to practical use. Priorities include multi-center trials, clear dose standards, and smarter applicators that watch reactive species and temperature in real time. As delivery improves and biomarkers guide who benefits most, CAP could become a low-toxicity add-on to cancer care, used alone for accessible lesions or as a force multiplier for surgery, drugs, and radiation.
