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Rare blood disorder treatable with targeted therapies

The hallmarks of the rare blood disorder, ALK-positive histiocytosis, have been unraveled in a new study. Targeted therapy works well in children and adults with the disease, the study shows. The condition was described in the leading journal Blood.

Histiocytes are white blood cells that are part of the immune system. In histiocytoses, a group of rare diseases, faulty white blood cells pile up in the body. Depending on the location in the body, these build-ups can lead to a range of symptoms, from a painful bump on the head or annoying skin abnormalities to excessive drinking and peeing. In the past, the disease has been mistaken for a form of leukemia.

New shape

A new form of histiocytoses was discovered in 2008, where there is a fault in the so-called ALK gene. In the new study, an international team of experts looked for the clinical, pathological and genetic characteristics of children and adults with this ALK-positive form of histiocytosis. Their goal: gaining knowledge to improve the diagnosis and treatment of future patients.

The new study was set up by doctors and researchers at the Princess Máxima Center, in collaboration with colleagues from 11 countries in Europe, North America and Australia. The research was published this month in the prestigious journal Blood.

Very rare

Paul Kemps is a medical researcher at the LUMC with a temporary guest appointment in the Princess Máxima Center with pediatric oncologist Cor van den Bos, and was involved in the study. 'Because ALK-positive histiocytosis is such a rare disease, little was known about the characteristics of children and adults with this condition,' he explains.

Data from 39 people with ALK-histiocytosis - the largest group of patients to date, including 31 children and 8 adults - were examined. Several children from the Máxima also took part in the study. The researchers studied at what the tumor cells look like genetically and under the microscope. They also looked at in which organs the cells had built up, and how patients responded to their treatment. In half of patients, the researchers saw a build-up of tumor cells in the brain, spinal cord or nerves in the body. Kemps: 'That shows that this is truly a separate form of the histiocytoses, with its own characteristics.'

Targeted treatment

Eleven patients in the study were given a drug that specifically matches the change in the ALK gene. Some of them had been treated with chemotherapy before, but it didn't work well enough. The targeted treatment was successful in all eleven patients, including ten patients with tumors in the nervous system. 'This underlines the effectiveness of this new therapy in the treatment of this rare disease,' Kemps says.

Creating awareness

Kemps: 'Although ALK-positive histiocytosis is rare, it is important for doctors to know that this condition exists. Our research also shows the importance of genetic analysis of tissues affected by histiocytoses, as it can have a direct effect on the diagnosis and treatment of the patient.'