In 2013, doctors in Medellin, Colombia, cared for a man with tumors in his lungs, adrenal glands and lymph nodes. He was HIV-positive and was not taking HIV medication, so he had a severely weakened immune system. Tissue samples showed the cancerous growths were not human.
DNA studies found that these cells were from an intestinal parasite known as dwarf tapeworm, which is found in warm climates and areas with poor sanitation. The patient ultimately died of kidney failure, but doctors suspect the tapeworm cells played a key role in his death.
This is the first known case of parasitic cells mutating to cause cancerous growths. It raises fascinating questions about the role of the immune system in cancer treatment and prevention.
It is not clear how common this condition is. For one thing, dwarf tapeworm infections are relatively unusual in developed countries with advanced water and sanitation systems.
Other parasitic infections have also been associated with cancer. For example, flatworms may lead to bile duct cancer or bladder cancer, and cause devastating disease. In such cases, cancer is thought to result from a combination of chronic inflammation and/or substances produced by the parasites that cause nearby human cells to become cancerous.
Human immune cells continually patrol the body, destroying foreign and abnormal cells. Many cancer therapies, both current and in development, seek to take advantage of this, either by directing immune cells against cancer cells or by stimulating the immune system to attack cancerous cells. It may be that a weakened immune system allows parasitic cells to transform themselves somehow into cancerous cells.
Research has found that people with weakened immune systems, such as HIV patients, have higher rates of cancer than the general population. But it's hard to know. In developing countries where both HIV and parasitic diseases are common, such parasite-cancer mutations may be common. But we don't know, and there is little money for research. So the ability to detect and study the interaction of parasitic diseases and cancer is severely limited.
Have similar cases of parasite transformation into cancerous cells in humans occurred many times before, without doctors noticing? Probably. At the least this new report could potentially help prioritize important public health problems.
The key lesson from this case is that we need to increase funding for research and public health in developing countries where neglected infectious diseases are common.
The prime example of this is the recent Ebola epidemic in West Africa, which killed over 28,000 people and terrified the world. The first case was confirmed by the World Health Organization a full three months after the actual epidemic started. This was enough time for the disease to spread far and wide, and to create a global threat.
Of course, parasites mutating into cancer cells is probably not a threat on the same level. But it may be much more common than we realize in some parts of the world. And we owe it to the people in those places to find out exactly what the risk is.
For the broader public, research into this area could provide much insight on the relationship between the human immune system and cancerous growth.