Hyperthermia is a type of treatment in which body tissue is heated to as high as 113 °F to help damage and kill cancer cells with little or no harm to normal tissue. Hyperthermia is almost always used with other forms of cancer treatment, and many clinical trials have shown that it can help shrink tumors and may make it easier for radiation and chemotherapy to kill cancer cells.

Since the 18th century, spontaneous remissions of cancer—altogether a very rare event—have been observed repeatedly in connection with febrile infectious diseases, especially those of bacterial origin. In the 1950s, Huth described 24 remissions of leukemia after bacterial infections, and Stephenson reviewed 224 spontaneous remissions of cancer, 62 of which occurred under infection or persistent fever.

In 1891, William B. Coley injected streptococcal organisms into a patient with inoperable cancer. He thought that the infection he produced would have the side effect of shrinking the malignant tumor. Over the next forty years, as head of the Bone Tumor Service at Memorial Hospital in New York, Coley injected more than 1000 cancer patients with bacteria or bacterial products.

This review summarizes historical reports linking feverish infection with tumor regression. It notes that spontaneous remissions were repeatedly observed with febrile infectious diseases and that Coley’s mixed bacterial vaccines were used in an attempt to reproduce those effects.

The American Cancer Society explains that "very high temperatures can kill cancer cells, but they also can injure or kill normal cells and tissues." It states that "sometimes, hyperthermia can be used to treat cancer effectively, particularly small cancers" and that in other situations "hyperthermia is not used alone to treat cancer" but "can be used with other types of treatment for different cancers." The ACS notes that local hyperthermia can destroy tumors without surgery, while regional and whole-body hyperthermia "seem to make other forms of cancer treatment work better" by making cancer cells easier to kill with radiation and certain chemotherapy drugs.

The review states that one of the best-known historical examples of inducing cancer regression is Coley’s toxin, which used heat-killed bacteria to provoke fever and immune activation. It also notes that case reports have described spontaneous regression of cancer after acute infection and fever, suggesting a possible link between infection-triggered immune responses and tumor shrinkage.

This 2024 review states that the therapeutic efficacy of hyperthermia "is generally observed between 40 °C and 45 °C" and that temperatures of "42.5 °C and above can destroy tumor cells." It explains that hyperthermia promotes cancer cell death by inducing oxidative stress, mitochondrial dysfunction, caspase activation, and PARP cleavage, and can cause G2/M cell cycle arrest and damage tumor vasculature. The authors emphasize that in clinical practice, hyperthermia "is most effective when combined with radiotherapy and/or chemotherapy" and that local heating of tumors to approximately 42 °C for 60 minutes enhances outcomes by directly killing tumor cells and sensitizing them to radiation and chemotherapeutic agents.

In this case-control study, researchers tested whether cancer patients had a different history of fever during infections than healthy controls. The authors report that cancer patients were more likely to say they did not experience fever during infections, while controls more often reported fever during illness.

Cancer treatments can cause a fever directly or destroy white blood cells and weaken the immune system. The page advises patients to call a doctor if they have a fever of 100.4 °F (38 °C) or higher, showing that fever after a cancer diagnosis is treated as a potential warning sign, not a cure.

Nauts tracked down case reports and long-term follow-up information on hundreds of patients treated with Coley’s toxins. She presented evidence that her father’s method had worked in a significant number of patients, and the toxins were effective at inducing fever and robust surges in cytokines.

This article reviews evidence that "recently accumulated evidence has shown that hyperthermia amplifies immune responses in the body against cancer while decreasing the immune suppression and immune escape of cancer." It states that survival of cells is reduced by heating at 39–42 °C and is "amplified remarkably by heating at ≥ 42.5 °C for ≥ 1 h," and that mild hyperthermia in the 39–42 °C (fever‑range) for 1–2 hours has been reported as useful in combination with other cancer therapies. The authors caution that "the anticancer efficacy of hyperthermia alone with currently available heating devices is not enough to suggest its use as a standalone therapy," but note that combination therapy with immunotherapy, radiotherapy, chemotherapy, and surgery improves anticancer efficacy in vitro and in vivo.

Fever therapy became a therapeutic modality in the early 20th century, when physicians tried to raise body temperature to fight cancer. The article also states that many of these approaches were later discarded, and that some fever machines were quackery devices used to fraudulently treat cancer patients.

This university news release describes research on hyperthermia in which tumors are heated to "fever temperatures of about 42 °C for 60 minutes or more." It reports that heating tumors can greatly enhance the effect of radio‑ and chemotherapies: the higher temperature ensures better blood circulation of the tumor and prevents cancer cells from recovering after treatment, thereby enhancing therapeutic efficacy without additional toxicity. The piece emphasizes that hyperthermia can substantially improve chances for disease‑free and long‑term survival or allow the use of lower doses of radiation and drugs, but refers specifically to controlled local heating of tumors rather than systemic fever.

In this expert interview, a radiation oncologist at Cleveland Clinic explains that hyperthermia therapy "uses heat to destroy cancer cells and shrink tumors" and that their center uses local or regional heating "as opposed to total body heating, such as seen in a fever." She states that hyperthermia can make radiation work about 50% better, and up to threefold better in re‑irradiation settings, with very few side effects. She also reports that phase III and other clinical trials have shown benefits of adding hyperthermia in many cancer types, including improved survival in sarcomas, ovarian and cervical cancers, glioblastoma, pancreatic and gastric cancers, as well as improved local control and pain control in certain settings.

This overview notes that "the principle behind hyperthermia therapy is that elevated temperatures can ablate or destroy cancer cells and enhance the effectiveness of conventional treatments like chemotherapy and radiation therapy." It explains that heat may cause cellular changes that kill cancer cells or make them more susceptible to chemotherapy and radiation. The article characterizes hyperthermia therapy as an innovative approach intended to improve cancer patient outcomes through controlled application of heat, distinct from naturally occurring fever.

This paper discusses epidemiologic observations that a history of infectious fever has sometimes been associated with reduced cancer risk or occasional tumor regressions, and revisits historical concepts of using fever in oncology. It emphasizes that contemporary oncology does not rely on spontaneous fever to treat cancer but instead develops controlled hyperthermia techniques, stating that modern controlled hyperthermia achieves reproducible temperature elevations and treatment schedules that historical fever therapy could not standardize. The authors call for more research into immune mechanisms activated by moderate fever but do not present evidence that ordinary fever in clinical practice reliably cures cancer.

This review examines experimental data on "fever‑range hyperthermia" (typically 39–41 °C) and its effects on tumors and the immune system. It reports that fever‑range hyperthermia can modulate immune responses, improve tumor perfusion and oxygenation, and enhance sensitivity of tumor cells to radiotherapy and chemotherapy in preclinical models. The authors note, however, that clinical application generally uses controlled hyperthermia devices and that there is limited direct clinical evidence that spontaneous fever episodes alone can eradicate established cancers.

Historical accounts describe occasional tumor regressions after feverish infections or induced bacterial therapies, but these reports do not establish that fever itself cures cancer. Modern oncology does not treat fever as a curative cancer therapy, and the evidence base is limited to historical case reports, small studies, and mechanistic hypotheses rather than definitive randomized proof.

Coley’s original idea was based on his observation of one patient whose incurable sarcoma regressed completely following a severe streptococcus infection. This mixture, now known as Coley’s toxins, caused fever and shivering that were clinically similar to the signs of true infection, and he then noted that some patients responded with complete tumor regression.

This white paper argues that fever is a natural curative response and that hyperthermia has efficacy as a cancer treatment, including claims of tumor shrinkage and improved outcomes. Because it is a company white paper, it is promotional rather than independent evidence.

The article says an immunological mechanism has been suggested for some reported cases of spontaneous remission and regression of cancer after an acute infection. This is presented as a hypothesis based on case reports rather than as established proof.