In research published in the New England Journal of Medicine on Wednesday, CDC officials have confirmed the first known case of cross-species cancer transmission. The disease, which was contracted by a Colombian man suffering from HIV infection, was caused by cancer cells developing inside a tapeworm living in the man’s intestinal tract. The cancer cells spread from the tapeworm to their host, and the man developed tumors throughout his body.
Local physicians biopsied the tumors in hopes of identifying their cause, only to discover the cells looked and behaved abnormally for cancer cells. The cells were smaller than typical cancer cells, but grew just as rapidly and were just as destructive.
Out of fear that the cells might belong to a new kind of infectious organism, the doctors contacted the CDC.
Samples of the cancer cells were passed on to Atis Muehlenbachs, a pathologist with the CDC team that investigates mystery illnesses and deaths. He and his team ran dozens of tests, during which they found that the cells contained pieces of DNA similar to those found in the dwarf tapeworm – a tapeworm commonly found in humans. They passed the results on to a tapeworm expert at the Natural History Museum in London, who confirmed the presence of the parasite’s DNA in the cancer cells.
“In the initial months we wondered if this was a weird human cancer or some unusual, bizarre emerging protozoa-amoeba-like infection,” Muehlenbachs told the Washington Post. “Discovering these cells had tapeworm DNA was a big surprise.”
It’s the first known case of cancer being transmitted from one species to another, but it’s not the first time cancer has been transmitted from one organism to another.
“The only thing I can think of that is pretty similar is the phenomenon of donor transmitted cancer in transplant [patients],” Dr. Alfred Neugut of Columbia University’s Medical Center told Healthline.
It’s not uncommon for cancer to go undetected and be transmitted from one person to another via an organ transplant, particularly once patients begin taking immunosuppressant drugs to prevent the body from rejecting the new tissue.
HIV has a similar effect on the immune system and, Dr. Muehlenbachs says, likely kept the Colombian patient’s body from removing the cancer cells before they could take root and grow into tumors throughout his body.
“We didn’t believe that cells from a human parasite could become malignant and then invade human tissue. It’s just very unusual that the parasite’s cells became cancerous inside a human and then invaded into human tissue,” Bobbi Pritt, director of clinical parasitology at the Mayo Clinic told the Washington Post.
Now that the illness has been identified, it’s not clear how many cases could potentially be out there, but many experts are weighing in, speculating that this may not be a one-off case. There could potentially be millions of people out there suffering from similar symptoms.
“[The tapeworm] is a very common infection in humans, and therefore I would expect there are to be other cases like the one described, that were misdiagnosed or went undetected,” Pritt says.
The tapeworm in this case, Hymenolepis nana, is very common in humans, particularly in developing nations where sanitation levels are very low, reports the Verge. The CDC estimates that around 75 million people are carrying this parasite at any given time. But for the most part, the tapeworm is relatively harmless, often going undetected in humans. The Colombian patient was something of a unique case, but as Bobbi Pritt cautions, this kind of illness could very well be more common than they expect, especially in nations without the medical or scientific facilities necessary to detect and diagnose the abnormal tapeworm-transmitted cancer cells.
[Photos by Getty Images]