In a strange collision of infectious disease and oncology, The New England Journal of Medicine (@NEJM) yesterday published a case report of a man who succumbed to cancer, which was surprisingly not his own, but his parasite’s.
This is by far not the first clash of the infectious disease and oncology fields. Researchers have been studying “oncogenic” viruses, those that cause cancer, for many years. This type of virus is perhaps exemplified by human papillomavirus (HPV), which causes cervical cancer in women and can also cause anal cancer in men who have sex with men. In fact, the impetus to develop the HPV vaccine was to reduce incidence of cancer, not necessarily limit genital warts, though that’s certainly a positive side effect of the vaccine.
Additionally, ID and oncology have gone hand-in-hand in the quest to understand immune surveillance. That is, how our body detects and eliminates foreign things like pathogens and stressed cells and tissues like cancerous ones. There is much more research to be done in this field, but it appears that the cell types and blood molecules involved are similar during both processes.
In their NEJM article, Atis Muehlenbachs and colleagues reported on a 41 year old HIV positive man who presented to a hospital in Columbia with fatigue, fever, cough, and weight loss. CT scans revealed nodules in his lungs, liver, and lymph nodes consistent with cancer. But upon closer inspection of the biopsies, the cells in the tumors were very strange. Over the course of a few months, this case puzzled all the doctors who took a look. And just 72 hours before the patient passed away–with no time left to save him–molecular tests unexpectedly identified the cancer cells as not the patient’s, but belonging to the tapeworm Hymenolepis nana.
H. nana is typically a gastrointestinal parasite that causes diarrhea. It’s ability to induce cancer in this patient is markedly different than HPV because HPV infects your cells and causes them to grow out of control. In this case report, the patient had within him tapeworm cells growing out of control and forming tumors.
Now you might wonder, why didn’t this man’s immune system detect and eliminate the tapeworm or its cancerous cells? Well, remember that he was also HIV positive. And he had progressed to AIDS because his CD4 T cell count was just 28 cells/mm3, which is extremely low. So his immune surveillance was broken, allowing not only the tapeworm to infect and live within him, but also allowing the tapeworm’s cancer to grow and spread.This is likely to be a very rare occurrence since tapeworm infection itself is rare outside of developing nations and in patients with immune compromise such as HIV infection. But what’s really cool about this case is the ability of the tapeworm to spread its cancer. How did the tapeworm cells break free of the worm itself and continue to thrive? Transmissible cancer has been reported in dogs and Tasmanian devils, but even in those cases, the tumors are composed of dog cells or Tasmanian devil cells. This case is not only evidence of transmissible cancer in humans, but transmission between markedly different species separated by at least 800 million years.
Now I can only hope this guy doesn’t give you nightmares.