Adrián Báez-Ortega
What do you think of the article as a whole? Is it of good quality?
‘Yes: the methods are sound and the genetic evidence supporting a common origin for the tumours found in different individuals is overwhelming. It is not possible to explain the study’s results unless one accepts that this cancer has been transmitted directly from one animal to another; what remains to be clarified is the route of transmission.’
How does this fit in with the evidence already known, and what implications might it have?
“Until about ten years ago, it was believed that transmissible cancer was an extremely rare phenomenon affecting only two mammalian species: dogs and Tasmanian devils. However, over the last decade it has been discovered that this type of cancer is quite common amongst marine bivalves (cockles, mussels and clams), to the extent that it seems possible this is a completely ordinary occurrence in these species. The fact that transmissible marine cancers are so widespread has also begun to suggest that the aquatic environment may be more conducive to the transmission of cancer between individuals, and this new example of transmissible melanoma in fish reinforces this hypothesis. “I believe it is highly likely that there are many other cases of transmissible cancer in the wild that have gone unnoticed until now due to a lack of research, particularly amongst aquatic invertebrates, which do not have an immune system as developed as that of vertebrates.”
Are there any significant limitations to bear in mind?
“Although the study design, the quality of the tissue samples and the quality of the DNA sequencing may not be entirely optimal in this case, the genetic evidence, as I mentioned earlier, is more than sufficient to accept a common origin for the tumours.”
Are there any cases of tumour transmission between humans? Could mechanisms similar to those described in some animal species occur in humans?
“There have been no cases of ‘epidemics’ of transmissible cancer, and it is highly unlikely that we will ever see anything of this nature, mainly due to the effectiveness of our immune system in detecting and rejecting cells from another person. For cancer to be transmitted between humans in the way it is occurring in other animals, there would need to be a specific subpopulation of individuals with a chronic immune deficiency, rendering them unable to reject this type of invasive cell. However, there have been isolated cases of cancer transmission from one individual to another, usually as a result of an organ transplant: if the transplanted organ contains dormant cancer cells from the donor, these cells are capable of ‘waking up’ and causing cancer in the recipient, because treatment for an organ transplant involves permanent suppression of the patient’s immune system.”