In a study published in Nature US scientists have found that just one skin cancer cell may be enough to generate an entire new tumour. This finding undermines hopes that only certain types of cell will cause spread of the disease.
The research team, from Howard Hughes Medical Institute and the University of Michigan, were studying the skin cancer, melanoma. Melanoma is well known for its ability to spread and cause terminal disease from a single site.
Normally the ability of a single cell to "seed" a new tumour is tested by injecting large quantities into mice with weakened immune systems and counting how many tumours emerge.
The relatively small proportion of tumours supported the view of many scientists that not all cancer cells could trigger a new tumour, and that this ability was confined to a smaller number of specialist "cancer stem cells".
However, Sean Morrison, who led the latest work, said that this approach was flawed because the mice still had some immunity to these human cancer cells, leading to a significant underestimation of their potency.
First his team injected melanoma cells into mice with even more severely weakened immune systems, and found that 250 000 times as many of them formed tumours.
When single melanoma cells were used, they discovered that roughly one in four of them went on to seed new tumours.
This appears to be the first time that research has shown that individual cells from human cancers can effectively form new tumours.
