Researchers have discovered for the first time a case of the transmission of cancer cells to humans by a tapeworm.
Scientists at the Center for Disease Control and Prevention (CDC) discovered a puzzling and disturbing new cancer-like condition in a 41-year-old man who fell ill via a common stomach worm.
This case – the first known case of the transmission of cancer cells by a parasite to humans – concerns an HIV-infected patient in Colombia who developed numerous large tumors in various parts of the body. Doctors conducted biopsies and found that their cells were destructively like cancer cells, but exhibited strange characteristics in other respects. For example, they were about 10 times smaller than normal human cancer cells. Doctors asked the CDC for help.
Atis Muehlenbachs, a pathologist with a special department that investigates unexplained mysterious diseases and deaths, was unsure what to think about the cell samples when he and his team received them. Their growth pattern corresponded to cancer, they were crowded and had a high proliferation rate. But they also fused together, which is rare for human cells.
Muehlenbachs said in an interview that one of the initial theories said it could be a new type of infectious organism. But after conducting dozens of studies, the team found that the cells contained fragments of dwarf tapeworm DNA, Hymenolepis nana. This analysis was confirmed by a scientist and tapeworm expert at the Natural History Museum in London.
“In the first few months, we wondered if it was some strange human cancer, or some new, unusual and bizarre disease like protozoa or amoebas,” she recalls. – The discovery of tapeworm DNA in these cells was a huge surprise.
Researchers at the CDC, who published their findings in the New England Journal of Medicine, now believe that the Colombian may have digested microscopic tapeworm eggs, most likely found in food contaminated with mouse, insect or human faeces. Because the male immune system was compromised, tapeworms rapidly multiplied in the digestive tract and cells spread to other parts of the body. It is unclear whether tapeworm egg cells showed cancerous properties before they even entered the male body, or whether some interaction between the parasite and the body made them acquire them later.
This is the first time that cancer cells from parasites have spread throughout the human body, Muehlenbachs said. – This is a very unusual, very unusual disease.
This case is of concern for several reasons.
We know that many animals, such as various sea creatures, are susceptible to cancer, while others, such as the elephant, are almost immune to it. But until now, scientists have not believed that any human parasite can have cancer cells inside it or pass them on to humans.
We also knew that certain parasitic infections could increase people’s risk of certain cancers. For example, a flatworm promotes cancer of the bile duct, and a river creature called a blood fluke promotes bladder cancer, according to the American Cancer Society. But the reason is quite different, namely an overactive immune system that can weaken the patient.
The presence of cancer cells in dwarf tapeworms also raises questions about the origins of the mutated cells and whether other organisms living in or derived from humans can transmit cancer cells. In recent years, many scientists have emphasized that the ecosystem of the human body is only 10 percent. consists of human cells, and 90 percent. from microbial cells.
“We did not believe that human parasite cells could become malignant and then invade human tissue. This is very unusual, said Bobbi Pritt, director of clinical parasitology at the Mayo Clinic in an interview.
But the idea that dwarf tapeworms are also susceptible to cancer makes some sense, Pritt said, because “every living animal is made up of cells that divide and can become cancerous.”
Cancer is generally not considered contagious, although there have been rare cases of human-to-human transmission of malignant tumors via organ transplants or mother to child during pregnancy. In addition, some animal species – such as Tasmanian devils and domestic dogs – are known to pass on cancer cells within the population. The CDC does not believe that there is any risk of transmission of tapeworm cancer cells directly from one person to another.
It is not known how common carcinoma of dwarf tapeworms is in humans, but experts like Pritt believe that there are more of these cases. “Infection with dwarf tapeworm is very common in humans, so I suppose there are other cases similar to this one that have been misdiagnosed or not detected,” he said.
Matthew B. Laurens, a professor at the University of Maryland School of Medicine who specializes in infectious diseases, said the findings described above highlight the need to improve cancer diagnosis and data collection in developing countries.
– It is possible that this is only the tip of a very important phenomenon – he said. (…)
The Colombian got the attention of scientists at the Universidad Pontificia Bolivariana in his hometown of Medellin when he saw his doctor because of fatigue, fever, cough and weight loss.
He has been living with HIV for at least 7 years and has received no therapy. Tomography showed tumors of varying sizes – from 0,4 to 4,4 cm – in his neck, lymph nodes, lungs, and liver. Stool samples showed the presence of dwarf tapeworms in the body.
Infection with dwarf tapeworms is very common in the world, especially in developing countries. It is estimated that 75 million people have them. Most show no symptoms and get rid of parasites quickly. But in immunocompromised people, dwarf tapeworms have excellent conditions and live in them for years.
Before CDC scientists found out what it was, the man’s condition had deteriorated and he was in a hospice. He died 72 hours later with no chance of treatment. The official cause of death was HIV / AIDS with cancer as a weakening factor.
Muehlenbachs said further research prevented the patient from dying and the fact that scientists were unable to grow tapeworm cancer cells in the lab.
Muehlenbachs is not sure if the available therapies could help him, given the nature of the tumors. According to him, traditional drugs for tapeworm infections – which fight their entire body in the larvae stage – might not work against tapeworm cancer cells. It is also unclear whether chemotherapy for normal human cancer cells would help shrink tumors.
The pathologist hesitated to call the Colombian’s disease “cancer” because his cells were different from normal human cancer cells, although they behaved similarly. Muehlenbachs describes his condition as “infection with cancer of parasitic origin which causes a cancer-like disease”.
According to him, the results of the CDC study are so unexpected that we lack precise terminology to describe them. – Can the tapeworm be said to have cancer? Defining it is a philosophical question. (…)