US researchers have found that just a single skin cancer cell is usually enough to trigger a whole new tumour.
For a long time, scientists have underestimated the power of some cancers to spread and cause new tumours, however, with the new study their undervaluation has been overpowered.
The new finding has ruled out any speculations that only certain types of cancer cell could fuel the spread of the disease.
To reach the conclusion, researchers from the Howard Hughes Medical Institute and the University of Michigan studied melanoma cancer, which is well known for its ability to spread lethally from a single site.
Usually scientists test the ability of a single cell to "seed" a new tumour by injecting large quantities into mice with weakened immune systems and then count how many tumours emerge.
And as the scientists came across a relatively small proportion of tumours, they got more evidence 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".
On the other hand, Dr Sean Morrison, who led the latest work, claimed that the new approach was flawed because the mice still had some immunity to these human cancer cells, and that's what led to a significant underestimation of their potency.
For the study, firstly, the researchers injected melanoma cells into mice with even more severely weakened immune systems, and found that 250,000 times as many of them formed tumours.
The scientist discovered that when single melanoma cells were used, around one in four of them went on to seed new tumours.
"As far as we know, this is the first time anyone has been able to show that individual cells from human cancers can efficiently form tumours," BBC quoted him as saying.
Thus, he said that identifying and targeting a small subset of these cells would reap no benefits.
"We think the underestimation of tumour-causing cells is a general problem in many cancers, not just specific to melanoma," he said.
Furthermore, he added that researchers were required to make their tests better to see if their cancers were equally potent.
Besides, his team used a battery of tests, but could not find anything marking out any of the cells as potential "cancer stem cells".
He claimed that despite the existence, the finding could indicated that some cancers, such as melanomas, were "good old-fashioned cancer", in which every cell was dangerous.
The study was published in the journal Nature.