New Type of Leukaemia Identified

Some infants with a type of leukaemia called acute lymphoblastic leukaemia (ALL) respond poorly to therapy. Now researchers have found that these patients actually have a type of leukaemia that is distinct from ALL, paving the way, they say, for targeted treatments.

ALL is a cancer of cells that develop into white blood cells. It is more common among children than adults and accounts for more than half of all childhood leukaemia's.

Researchers already knew that many ALL patients who respond poorly to treatment have a defect in the ``mixed lineage'' gene, which is located on chromosome 11.

Now with the help of gene chip technology, Dr. Scott A. Armstrong of the Dana-Farber Cancer Institute in Boston, Massachusetts, and colleagues have identified more than 1,000 genes that are expressed differently between ALL patients and patients with the mixed-lineage defect, suggesting it should be considered a distinct type of leukaemia.

Reporting in the advance online edition of Nature Genetics for December, Armstrong's team suggests that these patients should be classified as having ``mixed-lineage leukaemia'' (MLL) rather than ALL.

To determine whether MLL was a distinct form of leukemia, the researchers compared the expression of over 30,000 genes in 10 ALL samples and 17 MLL samples.

The investigators also compared genes expressed in ALL and MLL with those in another type of blood cancer called acute myelogenous leukaemia (AML); MLL cells have features similar to both ALL and AML cells. But they concluded that the diseases were ``three distinct entities.''

``We expected to find that a few genes would be different between MLL and ALL, but the number we found immediately suggested to us that we were dealing with a different type of leukaemia,'' Armstrong says.

``This is exciting,'' Armstrong continued. ``It's not your standard ALL, and this is probably why these leukaemia's don't respond well to ALL therapy.''

According to Armstrong, a physician cannot tell an MLL patient from an ALL patient without sophisticated genetic tests, since the symptoms are the same, but ``now that we know that MLL is distinct, we can start directing treatment with that in mind.''

He added, ``It won't immediately change the way we do things, but our ultimate goal is to develop new therapies based on the genes expressed in different types of leukaemia--ones that are less toxic and more specific.''