A cold environment, which is known to induce suppression of the anti-tumor immune response, was found to encourage cancer growth in an animal study published in the journal Proceedings of the National Academy of Sciences (PNAS)1.
When it gets cold, the human body gradually goes into survival mode, blood vessels narrow in order to maintain body heat and our extremities start to suffer. Our metabolism speeds up and we shiver. When it is very cold the body focuses on just keeping the brain, heart and other vital organs functioning at a cost to the rest of the body.
Kathleen M. Kokolus and team also found that a cold environment alters how cancer cells grow and metastasize (spread) in mice. The researchers say their finding has implications for cancer research using mice, as well as cancer therapies.
In most animal experiments the mice tend to be housed in colder-than-normal temperatures.
The team compared cancer progression and metastasis in mice housed at 22°C (72°F) and 30°C (86°F). They found that several types of cancers, including those of the pancreas, colon, skin and breast developed more rapidly and started spreading earlier and more aggressively in the colder environment.
The tumors grew more rapidly even in the mice that were used to cold temperatures - ones that had lived in the cold from the day they were born.
The human body's anti-cancer immune response is largely driven by T cells. T cells are a type of white blood cells we call T lymphocytes and are part of our immune system, they help the body fight diseases, including cancer.
Cancer cells try to outsmart T cells when they are attacked by releasing signals telling the body to suppress the T cells, the T cells respond with counter-measures.
This struggle continues until one of them - the T cells or the cancer cells - wins. Many cancer therapies are aimed at helping the immune system stay on top.
T cells are more effective when it is warm
The scientists, from the Roswell Park Cancer Institute, Buffalo, New York, explained that although both sets of mice had the same number of T cells before they developed cancer, the T cells in the animals housed in a warm environment were much faster and better able to burrow into the tumor to destroy it.
The T cells in the warm mice also secreted higher quantities of anti-cancer substances compared to those in the cold mice.
There were significantly more cells that suppress the anti-tumor response in the cold mice, i.e. the bodies of the mice in the cold environment were much more likely to accept the tumor than to fight it.
If most mice in research facilities are housed in colder-than-normal environments, findings may be distorted and possibly invalid.
In an Abstract in the journal, the authors wrote:
"Therefore, the common approach of studying immunity against tumors in mice housed only at standard room temperature may be limiting our understanding of the full potential of the antitumor immune response."
Mice with cancer seek out the hottest environment
If you give a group of mice the choice of five environments ranging in temperature from 22°C to 38°C, most of them will go for the "comfortable" 30°C one. Humans are similar; in the wintertime we all have our ideal setting for the thermostat. If the room temperature drops we get up and check the setting.
Mice with cancer, on the other hand, tend to prefer the warmest 38°C environment. Humans with cancer are more susceptible to feeling cold in "normal" temperatures, especially after receiving treatment.
The researchers suggest that cancer cells possibly induce cold stress in order to secure and promote their own survival. How and why this occurs is still unclear.
The authors wonder whether treating cancer patients in hot rooms might lead to better outcomes.
A study carried out by a team at the Institute for Hyperthermia and Immunotherapy, Windmühlgasse in Vienna, Austria, showed that hyperthermia with radiation therapy, chemotherapy or immunotherapy resulted in significant improvement in outcome2. (Hyperthermia is the condition of having a body temperature greatly above normal.)
The team emphasized the need for further studies.