The Centers for Disease Control and Prevention's "X-files" unit (the one that investigates unexplained illnesses and deaths) has made a mind-blowing discovery about tapeworms and their ability to transmit cancer to humans. The details, which were published in a case study in the New England Journal of Medicine on Monday and tell the story of a 41-year-old man in Colombia who developed multiple tumors all over his body from a common stomach bug, raise important questions about what this means for the rest of us. Below are some of the key points you need to know to understand the significance of the case.

1. The CDC is hesitant to call the illness the man got a true cancer because the malignant tapeworm cells look and act a somewhat differently from human cancer cells -- but practically speaking he did have cancer. The tapeworm cancer cells were as devastating to the man's body as normal human cancer cells and resulted in so many tumors growing in his lungs, liver, lymph nodes and other parts of the body that researchers say he would have likely died from them without effective treatment.

2. You shouldn't worry about becoming infected from tapeworm cancer cells by another human. Probably. Cancer has been shown to be transmissible in humans before but only in rare circumstances involving organ transplants or from a mother to a fetus during pregnancy. In animals, scientists have found only two contagious cancers so far. One is in dogs and non-fatal. The other is in Tasmanian devils. It is believed to be spread when the creatures, Australian marsupials, bite each other, and may be to blame for wiping out a large percentage of those creatures in the wild.

3. They don't know why the tapeworms cells mutated into a cancerous form. It could have been something in the environment -- after all, the World Health Organization has identified hundreds of carcinogens and many of them are industrial chemicals that are all over the earth these days -- or something unique to the patient like the combination of medications he was taking, or something completely different that we haven't thought of yet.

4. We didn't know until now that tapeworms could even get cancer and it's possible other parasites could, too. That's kind of worrisome because so much of our own bodies -- about 90 percent -- is made up of cells that aren't human. Cancer could theoretically impact any multi-celled animal but there hasn't been a lot of research on cancer and microscopic organisms.

5. There may be other undiagnosed or misdiagnosed cases of this type of tapeworm cancer. There are an estimated 75 million people living with tapeworm infections, most of them asymptomatic, and it's statistically probable or even certain that a number of them have cancer.  The only way to know for sure is by taking a biopsy that involves DNA sequencing, which is generally not done. CDC researchers say they don't believe this phenomenon is widespread, however, as the population of tapeworms inside the Colombian man's body may have only reached a critical mass because his immune system was compromised as he had HIV/AIDS. In a healthy person, the body is typically able to fight off tapeworm infections fairly quickly, so they may not have enough time to multiply and spread even if they were carrying cancerous cells.

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