Washington: Many older people have mutations linked to leukemia and lymphoma in their blood cells, scientists have found.
At least two per cent of people over age 40 and five per cent of people over 70 have mutations linked to leukemia and lymphoma in their blood cells, said researchers at Washington University School of Medicine in St Louis.
Mutations in the body's cells randomly accumulate as part of the ageing process, and most are harmless.
For some people, genetic changes in blood cells can develop in genes that play roles in initiating leukemia and lymphoma even though such people don't have the blood cancers, the researchers said.
The findings, based on blood samples from nearly 3,000 patients, don't mean that people with these genetic mutations are destined to develop a blood cancer.
In fact, the vast majority of them won't as the incidence of blood cancers such as leukemia or lymphoma is less than 0.1 per cent among the elderly, researchers said.
"But it's quite striking how many people over age 70 have these mutations," said senior author Li Ding of The Genome Institute at Washington University.
"The power of this study lies in the large number of people we screened. We don't yet know whether having one of these mutations causes a higher than normal risk of developing blood cancers. More research would be required to better understand that risk," Ding said.
The patients whose blood was analysed for the current study had been diagnosed with cancer but were not known to have leukemia, lymphoma or a blood disease.
They ranged in age from 10 to 90 at the time of diagnosis and had donated blood and tumour samples before starting cancer treatment.
Therefore, any mutations identified by the researchers would not have been associated with chemotherapy or radiation therapy, which can damage cells' DNA.
The researchers zeroed in on mutations that were present in the blood but not in tumour samples from the same patients. Such genetic changes in the blood would be associated with changes in stem cells that develop into blood cells, but not to the same patient's cancer.
They looked closely at 556 known cancer genes. In 341 patients ages 40-49, fewer than 1 per cent had mutations in 19 leukemia- or lymphoma-related genes.
But among 475 people ages 70-79, over 5 per cent did. And over 6 per cent of the 132 people ages 80-89 had mutations in these genes.
The researchers noted that nine of the 19 genes were mutated repeatedly, an indicator that the changes drive or initiate the expansion of blood cells with these mutations.
This expansion of cells is clearly not leukemia or lymphoma, the researchers said.
It may be a precursor to blood cancers in a small subset of patients, but the study was not designed to predict the future risk of developing these diseases, researchers said.