On Nov. 5, researchers from the U.S. Centers for Disease Control and Prevention (CDC) published a study about the malignant transformation of Hymenolepis nana or tapeworm in a human. The study focused on the recently discovered medical case that involved a 41-year-old male HIV patient in Columbia who died of tapeworm infection which resulted in the growth and spread of cancer-like cells in his body.

The discovery alarmed the medical community about the possibility of transferring cancer cells from one human to another through tapeworm. What does it mean for the general public? Is cancer contagious? Here are the key details from the CDC study:

  • Cancer is not contagious. As stated by the American Cancer Society, "Cancer cells from one person are generally unable to live in the body of another healthy person. A healthy person's immune system recognizes foreign cells and destroys them, including cancer cells from another person." Close contact, sexual intercourse, kissing or sharing meals with a cancer patient do not transmit the disease from one person to another.
  • Transmitted cancer cases are rare and usually involve mother-fetus transfers or organ transplants. However, it should be noted that organ donors go through meticulous screenings to diminish such danger. Patients who receive organ transplants need to take medication to pacify the immune system so it won't attack the foreign organ. A weakened immune system seems to be the major cause why a transplanted organ is able to cause cancer in the patient; however, such cases are very rare.
  • The malignant tapeworm cells found in the human host differ in some ways from actual human cancer cells, which makes the CDC somewhat uncertain to call the disease a "true cancer." However, just like the human cancer cells, the "tapeworm cancer cells" found did as much damage to the normal human cells. This led to the growth of numerous tumors in various parts of the human host which led to no possible treatment and to the patient's death.
  • The reason why the tapeworm cells mutated into malignant cells is still unknown. It could be due to a combination of medications the patient was taking when the infection occurred or something completely exclusive to the patient. The World Health Organization has a long list of carcinogens, many of which are man-made chemicals and can be found all over the world. Just recently, even red meat and the beloved bacon joined the carcinogens list.
  • Until recently, the scientific community wasn't aware that tapeworms can develop cancer. Mayo Clinic's clinical parasitology director Bobbi Pritt said they did not believe that parasite cells inside a human host can become malignant and attack human tissue. This raises concerns since hypothetically, any multicellular animal could be impacted. There are very few research done on microscopic organisms and cancer, which means there could be tapeworm cancer cases that are undiagnosed or worse, misdiagnosed.
  • H. nana (Hymenolepis nana) infects up to 75 million people at any given time, making it the most common tapeworm infection in humans. Symptoms are not seen in most people. However, "in people whose immune systems are weak, including people who have HIV or are taking steroids, the tapeworm thrives," wrote CDC in a press release.
  • The agency does not believe that the rare case is prevalent since the tapeworm clusters in the male patient were able to grow to such extent due to his HIV-weakened immune system. Theoretically, if a tapeworm inside a healthy human person was indeed carrying cancer cells, the immune system can kill the infection quickly before it can multiply.
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