Cancer cells deceive the immune system to avoid being destroyed.
Immunotherapy is growing in strength as a weapon against the disease, as research increasingly focuses on ways in which cancer apparently "tricks" the immune system into allowing it to develop.
One way in which cancer avoids the immune system is through "befriending" T cells, which seek out unwanted elements such as bacteria and viruses in the body's fight against disease, but mysteriously, do not attack cancer cells.In the 1990s, a molecule that Japanese scientists called "Programmed Death 1" (PD-1) was found on the surface of T cells. US researchers then found that cancer tumors often produced a matching molecule, "Programmed Death Ligand 1" (PDL-1). In this way, the cancer is able to "trick" the T cells into joining, instead of fighting it, thus circumventing the immune system.
This discovery led to the development of a group of drugs known as "immune checkpoint blockade therapies."
Another way in which cancers appear to subvert the immune system involves prostaglandin 2 (PGE2). PGE2 normally causes inflammatory response and fever in bacterial and viral infections, but it has been known for some time to promote tumor growth in the gastrointestinal tract.
One theory is that the inflammatory process does not always end when it should. Chronic inflammation can eventually cause changes, such as the formation of new blood vessels and DNA mutations, which can give rise to tumors. Cells involved in certain types of inflammation have been found to produce secretions that promote tumors.
Reawakening the immune system
According to the team from the UK's Francis Crick Institute, who carried out this project, PGE2 molecules "dampen down" the response of the immune system, which enables the cancer cells to "hide." If PGE2 molecules can be destroyed, they say, the immune system will "reawaken," find and kill the cancer cells.
Fast facts about cancer
- The four main cancers in the US are: breast, lung, prostate and colorectal
- There are around 1,658,370 new cancer cases expected in 2015
- This year, there are expected to be 589,430 cancer deaths in the US.
PGE2 in the body is produced by Cyclooxygenase, known as COX-1 and COX-2 enzymes. COX inhibitors are currently in the spotlight as a way to prevent the production of PGE2 in cancer patients. One way of inhibiting COX is through nonsteroidal anti-inflammatory drugs (NSAIDs), such as aspirin.
This study found that certain types of cancer in mice were substantially slowed by combining aspirin or other COX inhibitors with immunotherapy.
Given the "conservation of signature" across mouse and human melanoma, plus the fact that COX inhibitors appear to reduce gastrointestinal and breast tumors as well as melanoma, the team is hopeful that aspirin and similar drugs can be effectively used alongside current immunotherapy treatments to tackle bowel, breast and skin cancer.
Citing a study published in the Journal of the National Cancer Institute, the American Cancer Society suggest that low-dose aspirin could also be useful in treating and preventing recurrence of esophageal, ovarian, stomach and prostate cancer.
Concerns that regular low-dose use of aspirin can increase the risk of cardiovascular problems or internal bleeding in cancer patients with gastrointestinal problems have not been definitively proven, according to the US National Cancer Institute.
As Peter Johnson, Cancer Research UK's chief clinician, notes regarding the current research, "there is still some way to go [...] but it's an exciting finding that could offer a simple way to dramatically improve the response to treatment in a range of cancers."
Last month, Medical News Today reported that the use of aspirin or NSAIDs may be linked to reduced risk of colorectal cancer.