June 22, 2016

expert reaction to study looking at cancer transmissible between individual mussels, cockles and golden carpet shell clams

A paper published in the journal Nature has reported the identification of cases of cancer being transmitted from individuals in mussels, cockles and golden carpet shell clam species.

Prof. Mel Greaves, Director of the Centre of Evolution and Cancer at the The Institute for Cancer Research, London, said:

“This study looked at cancer cells in mussels, cockles, and golden carpet shell clams.  Obviously, humans are very different from shellfish in complexity, breeding patterns and lifestyle so the results are not directly applicable to cancer in patients, and are no cause for concern.

“Previous research has demonstrated transfer of cancer cells between individuals in dogs (where it is transmitted by sex) and in Tasmanian Devils (where it’s transmitted by biting). The possibility of transmission between humans is hugely limited by the fact that we are an outbred species and any cells that do get transmitted should be rejected immunologically, as foreign.

“There are very special and, fortunately, extremely rare circumstances where cancer transmission is possible in people. We showed some years ago that when childhood acute leukaemia occurs in both siblings in an identical twin pair, the explanation is that the leukaemia starts in one twin, in the womb, and spreads to the other via their joint circulation in the placenta. As they are genetically identical it cannot be rejected. This story was covered in the media at the time; this is not a new finding.

“There are also around 30 cases in the literature (over many decades) of what appears to be mother to foetus transmission of cancer – usually melanoma or leukaemia. A couple of years ago we used genetic markers to prove that in one case the baby’s leukaemia was indeed maternal in origin. Moreover, the cancer cells had deleted the maternal antigens (HLA) which rendered the cancer cells invisible to the immune system. This paper attracted widespread media attention at the time, worldwide; again, this is not a new finding.

“There are also several cases in the literature, over the past 40 years, of transplant recipients developing cancer that originated in the organ (kidney) donor. It’s still a very rare outcome of a transplant and happens less often now with more careful donor selection. The transmission was possible because of the route provided by the procedure AND the fact that the recipients where medically immunosuppressed.

“So, in all three cases, transmission was possible because a blood route for cancer cells was available AND the immune system was compromised. This risk is very, very small indeed.

“Regarding these new results in shellfish, the public should not be at all alarmed as the processes involved are different from those in people. The biology is however very interesting with implications for the evolution of both cancer cell clones and immune recognition within and between species.”

‘Widespread transmission of independent cancer lineages within multiple bivalve species’ by Michael J. Metzger et al. published in Nature on Wednesday 22 June 2016. 

Declared interests

None received.