In a discovery that baffled medical experts, the tumours within a 41-year-old Colombian man’s lungs were found not to have come from him, or let alone be human: they were actually from a parasitic tapeworm that had been living inside him. Doctors had previously attempted to diagnose the man back in 2013 and only with the combined efforts of the US Centers for Disease Control (CDC) and the UK’s Natural History Museum was the true reason uncovered.
Initial confusion arose when the apparently normal tumours were inspected closely to find that the cells were far too small (ten times in fact) to be human, leading to several theories from shrinking human cancer cells to a new type of infection. This prompted the Columbian doctors to contact the US CDC, for fear of an emerging protozoa or amoeba-like infection. Eventually molecular testing on the cells revealed high levels of tapeworm DNA, to everyone’s shock. Dr Atis Muehlenbachs, of the CDC, remarked that “it didn’t really make sense”. Unfortunately, by the time the doctors realised the origin of the man’s cancer, it was too late to treat him effectively. He died in Medellin, Columbia, three days after the discovery was made.
The tapeworm in this case was Hymenolepis nana, the dwarf tapeworm, a specialism for Dr Peter Olsen of the Natural History Museum, who notes that the worm is unique for its ability to carry out its entire lifecycle within a single organism. This property and the fact that the man had HIV, which weakened his immune system, meant that the worm could proliferate within his body without being destroyed, and so mutations could build up, leading to some of the worm’s cells to become cancerous. It is thought that rather than the worm itself getting cancer and that spreading to the patient, one of the thousands of eggs that it produces every day may have been able to penetrate the lining of his intestines and mutated into a cancerous cell, dividing and spreading to his lungs and lymph nodes.
A case of tumours originating from a parasite had never been found before, however with Hymenolepis nana being the most common tapeworm in humans (infecting up to 75 million individuals worldwide at any one time) and 35 million people suffering from AIDS in 2013, it is possible that there are undiagnosed cases out there right now. However, even if the diagnosis could have occurred sooner, it is unclear what treatment would have been appropriate for this situation.
There is debate over whether it can even be termed ‘cancer’ – they are calling it “an infection with parasite-derived cancer which causes a cancer-like illness”. The discoveries from this case show that there is still much to be researched, especially in the relatively new and rapidly expanding field of cancer biology.
Photograph: Mdbeckwith via Wikimedia Commons