In January 2013, a Colombian man who had been diagnosed with HIV was hospitalized with a fever, trouble breathing and tapeworms throughout his body.
Doctors noticed he had unusual-looking tumors in his lungs.
"It looked like cancer, but the tumors were composed of cells that were not human," Dr. Atis Muehlenbachs, a pathologist at the Centers for Disease Control and Prevention, told NPR.
Though physicians were initially baffled, DNA tests confirmed that the tumors were tapeworm cells. The tapeworms inside the man’s body had developed cancer, which had then spread to their human host. The case is the first of its kind.
"We knew invertebrates can grow tumors, but the fact that one can invade and disseminate in a human and make them sick just really, really defied belief," Muehlenbachs said.
“This is the first time we've seen parasite-derived cancer cells spreading within an individual," he told The Washington Post. "This is a very unusual, very unique illness."
Though tapeworms don’t typically cause issues like this, Peter Olson, a biologist at the Natural History Museum in London who was involved in the case, said it was something of a perfect storm.
"When your immune system gets compromised, you're in for all sorts of trouble,” he told NPR.
"It speaks of the commonality across the biological world,” he added. "So it shows that malignant transformation ... whether that's involving our own cells or those of a parasitic worm, may be the result of mutations to the same genes."
The man died within 72 hours of the diagnosis being made.
"When he was so sick and so tired, because he had spent several months at the hospital, he dropped all his hope," said Dr. Carlos Agudelo, an infectious disease doctor at the Bolivariana University in Clinic in Medellin, Colombia.