Unsettling finding from CDC:Tapeworms can transmit cancercells to humans

This common parasite, known as the Hymenolepis nana or the dwarf tapeworm, may carry cancer cells

that might take root in people with weakened immune systems. The malignant cells are pictured here.

Photo: Centers for Disease Control and Prevention via Washington Post

WASHINGTON — Scientists from the Centers for Disease Control and

Prevention have identified a puzzling and unsettling new cancer-like condition in

a 41-year-old man, who is believed to have become ill through a common

stomach bug.

The case — the first known transmission of cancer cells from a parasite to a

human — involves an HIV patient from Colombia who developed multiple, large

tumors in various parts of his body. Local doctors biopsied those tumors and

found that the cells acted like cancer cells in their destructiveness but were

strange in other respects. For one, they were about 10 times smaller than

normal human cancer cells. The doctors contacted the CDC for help.

By Ariana Eunjung Cha, Washington Post on 11.25.15

Word Count 1,272

Atis Muehlenbachs, an agency pathologist in the special unit that investigates

unexplained mystery illnesses and deaths, wasn't sure what to make of the cell

samples when he and his team received them in 2013. The cells' growth pattern

was cancer-like, they noticed, with overcrowding and a high rate of

multiplication. But the cells also fused together, which is rare for human cells.

One early theory, Muehlenbachs said in an interview Nov. 4, was that they could

be a new type of infectious organism. But after performing dozens of tests, the

team discovered the cells contained DNA snippets of a dwarf tapeworm,

Hymenolepis nana. That analysis was verified by a researcher and tapeworm

expert at the Natural History Museum in London.

"In the initial months, we wondered if this was a weird human cancer or some

unusual, bizarre emerging protozoa-amoeba-like infection," he recalled.

"Discovering these cells had tapeworm DNA was a big surprise — a really big

surprise."

The CDC researchers, who published their findings Nov. 4 in the New England

Journal of Medicine, now think the Colombian man might have ingested some

microscopic tapeworm eggs, most likely in food contaminated by mouse

droppings, insects or human feces. Because of the man's compromised

immune system, the tapeworms multiplied rapidly inside his gastrointestinal

tract and the cells invaded other parts of his body. It's unclear whether the cells

in the tapeworm eggs exhibited cancer-like properties before they entered the

man's body or whether some interaction between the parasite and his body then

caused them to become cancerous.

"This is the first time we've seen parasite-derived cancer cells spreading within

an individual," Muehlenbachs said. "This is a very unusual, very unique illness."

The case study is worrisome for numerous reasons.

We know that many creatures, such as various sea animals, are susceptible to

cancer, while others, like elephants, are almost immune to it. But until now,

scientists had not believed that any human parasite could harbor cancer cells or

transfer them to people.

We've also known that certain parasitic infections could put people at higher risk

for specific cancers — such as flatworms for bile duct cancer or a river creature

called Schistosoma haematobium for bladder cancer, according to the

American Cancer Society. But the reason was wholly different, namely a hyper-

immune response that could weaken an individual.

The presence of cancerous cells in tapeworms also raises numerous questions

about where the mutant cells originated — from something in the environment?

— and whether other organisms that live inside or on people could transmit

cancer cells. In recent years, many scientists have emphasized that the human

body's ecosystem is made up of only 10 percent human cells but 90 percent

microbial cells.

"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, said in an interview.

Yet the idea of tapeworms also being vulnerable to cancer makes some sense,

Pritt said, as "every living animal is made up of cells that divide and could

become cancerous."

Cancer is generally not considered to be a transmissible disease, although

there have been very rare cases of humans passing on malignant cells to other

humans through organ transplants or from mother to fetus during pregnancy.

There are also some animal species — such as Tasmanian devils and domestic

dogs — that are known to have transmissible cancer cells circulating within their

populations. The CDC does not believe there is any risk of the tapeworm cancer

cells being spread directly from one person to another.

It's unclear how common this type of tapeworm cancer illness is in humans, but

experts like Pritt believe it's likely that there are more cases out there: "H. nana is

a very common tapeworm infection in humans, and therefore I would expect

there to be other cases like the one described ... that were misdiagnosed or

went undetected."

Matthew B. Laurens, an associate professor at the University of Maryland

School of Medicine who specializes in infectious diseases, said the findings

highlight our need to strengthen cancer diagnosis and data collection in

developing countries.

"We could just be scratching the surface of something that could be very

important," Laurens said.

Peter D. Olson, a researcher at the Natural History Museum in London who

helped the CDC interpret its results, said that the finding represents "an

enormous advance in our knowledge and raises questions about the conditions

under which cells may become cancerous."

The Colombian man came to the attention of researchers at the Pontifical

Bolivarian University in his hometown of Medellin when he sought care because

of fatigue, fever, a cough and weight loss.

The patient had been living with HIV for at least seven years and had not been

adhering to therapy. A CT scan showed tumors ranging in size from 0.4 to 4.4

centimeters in his neck, lymph nodes, lungs and liver. Stool samples showed

tapeworms inside his body.

Tapeworm infections are very common worldwide, especially in the developing

world, with an estimated 75 million people infected with H. nana at any given

time. Most do not show symptoms and clear the parasites quickly. But in people

with compromised immune systems, tapeworms tend to thrive and can live in

their hosts for years.

By the time the CDC researchers figured out what was going on, the man's

condition had deteriorated and he was in hospice care. He died 72 hours later,

without any opportunity for treatment. His official cause of death was HIV/AIDS,

with cancer a contributor to his weakened state.

Muehlenbachs said further study was limited by the patient's death and the fact

that researchers have been unable to grow tapeworm cancer cells in the lab.

Muehlenbachs said he's not sure the current arsenal of treatments could have

helped given the nature of the man's tumors. He said traditional drugs to treat

tapeworm infection — which target the whole organism at the larval stage —

might not have been effective against tapeworm cancer cells, and it's also

unclear whether chemotherapy for normal human cancer cells could have

helped shrink the tumors.

In fact, the pathologist is cautious about calling the Colombian's illness "cancer"

because those cells were different from normal human cancer cells, even

though they behaved similarly. Instead, Muehlenbachs referred to it as "an

infection with parasite-derived cancer which causes a cancer-like illness."

He said the CDC investigation's findings are so unexpected that we lack the

precise terminology to describe it: "Can you say a worm has cancer? That's a

philosophical question how you define this."

While he believes this type of case is rare, no one knows for sure.

Muehlenbachs said further investigation is needed to determine whether it is

limited to tapeworms or whether the situation is worse — that there's some

"underlying biological phenomena" that might lead to transmissible cancer cells

developing in other creatures that can pass them along to humans.

Quiz

1 Which of the following sentences from the article shows how scientists revise their

hypotheses in light of new information?

(A) The cells' growth pattern was cancer-like, they noticed, with

overcrowding and a high rate of multiplication. But the cells also

fused together, which is rare for human cells.

(B) "In the initial months, we wondered if this was a weird human

cancer or some unusual, bizarre emerging protozoa-amoeba-like

infection," he recalled. "Discovering these cells had tapeworm DNA

was a big surprise — a really big surprise."

(C) "This is the first time we've seen parasite-derived cancer cells

spreading within an individual," Muehlenbachs said. "This is a very

unusual, very unique illness."

(D) Cancer is generally not considered to be a transmissible disease,

although there have been very rare cases of humans passing on

malignant cells to other humans through organ transplants or from

mother to fetus during pregnancy.

2 Which of the following aspects of the article is NOT thoroughly discussed?

(A) how scientists discovered tapeworm DNA in the cancer cells

(B) why scientists were surprised to find parasite-derived cancer cells

(C) why scientists were prompted to further investigate the cancer cells

(D) how scientists changed their beliefs after discovering the cancer

was from a tapeworm

3 Which of the following statements accurately represents the relationship between

the article's central ideas?

(A) Scientists have identified a puzzling new cancer that was

transmitted from a tapeworm to a human; as this is the first known

case of transmission from a parasite, the discovery has prompted

further investigation within the scientific community.

(B) Scientists have identified a puzzling new cancer that was

transmitted from a tapeworm to a human; however, the patient's

health was weak even before the tapeworm caused cancer so this

case may not be relevant in the future.

(C) The first known case of cancer transmission from a parasite to a

person has has prompted further investigation within the scientific

community; however, the death of the first patient has become a

major obstacle.

(D) The first known case of cancer transmission from a parasite to a

person has has prompted further research in the scientific

community; fortunately, these efforts have led to recent advances in

the treatment of cancer.

4 Which paragraph BEST develops the central idea that this cancer has never been

seen before?

(A) We've also known that certain parasitic infections could put people

at higher risk for specific cancers — such as flatworms for bile duct

cancer or a river creature called Schistosoma haematobium for

bladder cancer, according to the American Cancer Society. But the

reason was wholly different, namely a hyper-immune response that

could weaken an individual.

(B) Scientists from the Centers for Disease Control and Prevention have

identified a puzzling and unsettling new cancer-like condition in a

41-year-old man, who is believed to have become ill through a

common stomach bug.

(C) "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, said in an interview.

(D) It's unclear how common this type of tapeworm cancer illness is in

humans, but experts like Pritt believe it's likely that there are more

cases out there: "H. nana is a very common tapeworm infection in

humans, and therefore I would expect there to be other cases like

the one described ... that were misdiagnosed or went undetected."