A man has died as a result of tapeworm tumors growing inside his body, doctors report.
The 41 year old Colombian patient had HIV and therefore a weakened immune system, meaning the worm cancer was able to flourish inside his body.
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The report, which was published in the New England Journal of Medicine, is the first to describe a person having cancerous parasitic worm tissue growing inside their body and initially doctors were baffled as to what could be wrong with the man.
When the tumors were first found, they appeared to be normal. Some were more than 4cm in diameter and they were growing in the lungs, liver and other areas of the patient’s body. However, on closer examination, doctors realized that the cancer cells were of non-human origin. The invasive behavior and morphologic features of the cells were typical of cancer, but they were only one tenth the size of a human cell.
Atis Muehlenbachs, who picked up on the case at the US Centers for Disease Control (CDC), says:
It didn't really make sense. This had been the most unusual case, it caused many sleepless nights.”
Muehlenbachs considered several possibilities, including the shrinking of human cancer cells and the discovery of a new infection. The CDC and the UK’s Natural History Museum collaborated to try and diagnose the unusual cancer after Colombian doctors failed to do so in 2013.
Much to the surprise of Muehlenbachs, a polymerase-chain-reaction (PCR) assay eventually identified high levels of tapeworm DNA in the tumors. The tumor tissue came from the dwarf tapeworm Hymenolepis nana (H.nana) – a specialism of Peter Olson from the Natural History Museum. "There is something very special about this species," he says, "It is able to carry out its whole lifecycle in one host and that is absolutely unique."
The worm’s body releases thousands of eggs into the gut of its host every day and doctors believe that one of the eggs penetrated the patient’s gut lining and mutated, eventually forming cancerous tissue.
They were dividing and proliferating out of control and that is really what defines a cancer so they had a tape worm tumor."
By time doctors had clarified the cause of the tumors, the man was too unwell to be treated and he died three days after the worm DNA was discovered.
H.nana infection is though to occur in 75 million people at any given time and although worm cancer is rare, doctors are aware that cases could be going undiagnosed. The CDC recommends preventing infection by people ensuring they cook any raw vegetables and always wash their hands.