Researchers have for the first time shown that many people have cells in their blood which appear identical to leukaemia and yet the risk of developing the disease for most is virtually zero.
This has prompted the question that while early detection of cancer greatly improves the chances of successful treatment, is it possible that some cancers are being detected too early?
Chronic lymphocytic leukaemia (CLL) is the most common leukaemia in the western world and is often detected in people who do not have any symptoms. Only about half of these people will ever need treatment with chemotherapy for CLL. For those who never develop symptoms the greatest problem is the stress and anxiety associated with a diagnosis of leukaemia.
Using a common blood test, it is possible to detect CLL-like cells in about one in 20 adults. Fewer than one in 1,000 adults will develop CLL, and therefore many scientists thought that these leukaemia-like cells would turn out to be a rare but otherwise normal cell type which should be readily distinguishable from CLL.
However, studies funded by Leukaemia Research and published in the New England Journal of Medicine demonstrate that these cells are abnormal in many ways. In fact, the leukaemia-like cells so closely resemble CLL that the most advanced techniques cannot tell them apart.
Dr Andy Rawstron, who led the research, said: "The only clear difference from CLL is that these cells do not multiply and expand over time."
The researchers at the Leeds Teaching Hospitals then went on to assess the risk factors for developing progressive disease by reviewing the outcome for several hundred individuals diagnosed with CLL between 1995 and 2000 but with relatively low levels of CLL cells in their blood. Fewer than one in 10 required chemotherapy.
As the first study to provide five-year outcome data for this group of patients, the information has been central to changing the diagnostic criteria for CLL. Between 500 and 1,000 people per year in the UK with lower levels of CLL cells will no longer be classified as having leukaemia.
Dr Rawstron said: "It is now inevitable that routine blood tests identify individuals with leukaemia-like cells. As a result of this study we have a better understanding of the risk of disease progression for individuals with early stage CLL. We can use this information to minimise unnecessary stress and anxiety. For individuals with very low levels of CLL-like cells in their blood the risk of developing the disease is virtually zero."