Although Henrietta Lacks died of cancer almost 60 years ago, in a way, she still lives on. Prior to her death in the early 1950s, her cancer cells were collected by her doctor and grown outside of her body in a laboratory. Over the years, HeLa cells (as they were called to protect her identity) have been used for many experiments resulting in some very important scientific breakthroughs, such as development of a polio vaccine. These cells are special because, unlike most human cells, they are immortal. They have no limit (Hayflick limit) to cell division. Consequently, they reproduce and multiply is such a way that makes them relatively easy to grow in a tissue culture. They have evolved into what some consider a new species with an erie independence that can, at times, even be disruptive to researchers. HeLa cells have been known to contaminate other cell lines and grow "wild" within laboratories. While normal human cells have 46 chromosomes (23 pairs), HeLa cells have 76-80 chromosomes. When planted into animal tissue, HeLa cells can grow and produce a tumor, demonstrating that cancers can be transmissible. In general, other types of cancer cells share this pervasive behavior and immortality with HeLa cells. This has tragically been observed when human cancers are accidentally passed on to others from transplanted organs. While HeLa cells and other human cancers are transmissible only by artificial means (as far as we know), Devil facial tumor disease (DFTD) is an example of transmissible cancer that occurs in nature. This transmissible cancer of the grumbly little marsupials down under known as the Tasmanian Devil may severely imperil their populations. When devils bite each other, they pass on these cancer cells, which are derived from Schwann cells that normally support nerve cells. The devil's tumor cells have fewer chromosomes than the normal cells (13 instead of 14). Dogs also suffer from a form of transmissible cancer call Canine Transmissible Venereal Tumor (CTVT). Unlike devils, this cancer is sexually transmissible between dogs. Of course, the transmissibility of cancer agents is well known and widespread and not new. Viruses such as Hepatitis B, Hepatitis C, HPV and many others are known to cause cancer. However, this is quite different from transmissible cancers where the cancer cells themselves (rather than a virus) are passed on from one body to the next and continue dividing uncontrollably.
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