It has long been believed that cancer of any kind is not contageous or transmissible. This claim, however much intended it is to assuage the worries of cancer care-givers, is not necessarily true. A case in point is that of the highly contageous facial cancer of the Australian marsupial known as the Tasmanian Devil. Numerous other cases have been reported, including animal-to-human (the case of Harry Hall and his dog with cancer), human-to-human, and some speculate that even plant cancers can also be transmitted to humans and other animals. This tramsmissibility may be rare, but it should be acknowledged so that precautions can be taken to minimize the probability of transmission among those working with humans, animals, and plants with cancer.
There are also reported cases of cancer being unintentionally "seeded" or transferred within a patient when biopsies are performed and a few cancer cells are rubbed off the end of the needle during the transit of the needle as it is being withdrawn through other tissue.