A new test could help doctors decide which patients with chronic lymphocytic leukemia (CLL) will need treatment.

The test, which measures the presence or absence of a protein called ZAP-70, was described in The Lancet (Vol. 363, No. 9403: 105-111) by researchers from Britain and the US National Cancer Institute. People who have the protein are more likely to need treatment.

CLL is a cancer of bone marrow cells (lymphocytes) that is found mostly in older people. Many patients with this disease can live quite a few years without treatment, and survive many years after diagnosis. Others, though, have disease that rapidly progresses and leads to death within several years.

The problem facing doctors has been how to distinguish between these two groups of patients. When first diagnosed, the leukemia cells look similar, and decisions about treatment are based on the doctor's judgment about how the disease is progressing and whether it is causing symptoms.

Recently, though, scientists have discovered that changes in the DNA of the leukemia cells are responsible for the different courses of the disease. If the CLL cells have undergone a change in their DNA (mutation) that is seen in normal lymphocytes, patients may never need treatment. If the cells do not mutate, though, patients are more likely to have aggressive disease.

Earlier studies suggested ZAP-70 might be a good marker for this mutation.

The British and American researchers measured ZAP-70 protein in the cells from 168 patients with CLL, most of whom had been diagnosed many years before. The presence or absence of ZAP-70 correlated with whether the cells' DNA had mutated, and with how long the patients survived.

People without ZAP-70 in their CLL cells were more likely to have mutations, and lived anywhere from 15 to 34 years after their diagnosis. Their average survival was 24.4 years. On the other hand, CLL patients whose cells contained ZAP-70 were less likely to have mutations and lived from 7 to 11.5 years, with an average of 9.3 years.

The test for ZAP-70 is an important discovery because it is an easier way to look for signs of these mutations, and appears reliable. The technique is widely available in medical laboratories; previous methods for identifying DNA changes were much more complex and available only in specialized labs.

The study authors acknowledge that their finding raises many questions. They couldn't explain why certain cells had ZAP-70, or what specific role the protein may play in the disease. Is it responsible for the shorter survival of patients who have it? Much more research is needed to understand those questions.

Nevertheless, they say that by measuring this protein, doctors can reliably predict the course of their patients with CLL, which may translate into treating the appropriate patients.