Tapeworm Infection Turns Cancerous in Man With HIV

Fran Lowry

November 04, 2015

A unique clinical case shows that cells from a common tapeworm can proliferate and cause tumors once the parasite grows in people with weakened immune systems.

The case is described by researchers from the Centers for Disease Control and Prevention (CDC), in Atlanta, Georgia, and was published November 5 in the New England Journal of Medicine.

The discovery was made after studying a 41-year-old man from Medellin, Colombia. The patient, who was already immunosuppressed because of HIV, became the unwitting host of the dwarf tapeworm, Hymenolepis nana, which grew to such an extent that it spawned malignant cells of its own.

"We have a unique case in an immunosuppressed individual where he developed tumors where the cells responsible came from a tapeworm, so that they were indeed cancer cells, but derived from the tapeworm," lead author Atis Muehlenbachs, MD, PhD, staff pathologist at the CDC's Infectious Diseases Pathology Branch, explained to Medscape Medical News.

"This is a rare disease," Dr Muehlenbachs continued. "We don't know how rare, but of note, this tapeworm is the most common human tapeworm in the world, and also HIV and other forms of immunosuppression are common, so we encourage awareness of this disease and, in particular, that there is a risk of misdiagnosing it as human cancer. It is not human cancer. It's more of an uncontrolled infection from a tapeworm cancer that is growing inside the host, which in this case is a human being."

Top-notch Detective Work

Dr Muehlenbachs and his team did a lot of sleuthing to discover what was going on in this patient after they were approached by the man's doctors in Columbia for help in evaluating strange- looking biopsy samples taken from his lymph nodes and lung.

Dr Atis Muehlenbachs

"It took a long time to first figure out that these cells were not human cells, that they were not from an unusual, strange organism but were indeed from a tapeworm. We noticed that the morphologic features and invasive behavior of the cells were characteristic of cancer, but the cells were very small, about 10 times smaller than a normal human cancer cell. Eventually we were able to provide a diagnosis, but unfortunately, the patient was too sick to treat at that time," he said.

"It was an interesting day when we finally found out what was really happening. There was a sense of discovery. But I should tell you that there was also tragedy involved, because we had fought so hard. It was an uphill battle to determine if these were human or nonhuman cells. Discovering that they were from a tapeworm came as a big surprise, but by then, too many months had gone by, and we weren't even able to make a difference in the patient, who died 72 hours later," Dr Muehlenbachs added.

The researchers hope that this case will spark a deeper exploration of the relationship between infection and cancer.

"We would like to see increased awareness that this can occur, find new cases and see if they can be treated, and also find out more about whether similar disease processes may occur in other parasitic infections," Dr Muehlenbachs said.

Whether to treat this disease as an infection or as cancer is a great question without an answer as yet, he said.

"We don't have any other cases like this, but albendazole [Albenza, Amedra Pharmaceuticals LLC] would be a drug of choice for these invasive larval stages of tapeworms, although there is some evidence that it may not work for clonal proliferations of tapeworm stem cells. Cancer chemotherapy might work, but I can't even guess what type of regimen would be used. Another possible treatment to try would be antiretrovirals," Dr Muehlenbachs said.

Dr Muehlenbachs reports no relevant financial relationships.

N Engl J Med. 2015;373:1845-52.

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