Parents who smoke may contribute to genetic changes in their children that are associated with the most common type of childhood cancer, a study suggests.

Previous research has linked parental smoking to an increased risk of childhood leukemia, but with less consistent results for mothers than for fathers. The study is the first to link smoking by both parents to specific genetic changes in tumour cells of children with acute lymphoblastic leukemia (ALL), said University of California San Francisco’s Helen Diller Family Comprehensive Cancer Center researcher Adam de Smith, the lead study author. 

“We are seeing evidence of the toxic effects of tobacco smoke in the genes of the leukemia cell, a molecular type of forensic pathology,” says de Smith. “These deletions are not inherited from parents but are acquired in the child’s immune cells, so we think the more important windows of tobacco exposure are during pregnancy and after birth,” he added.

The researchers examined data on pre-treatment tumour samples from 559 ALL patients in a study of childhood leukemia cases in California. They wanted to see if any of the eight genes that are often deleted in ALL patients were missing in the tumour samples, and whether any of these deletions were associated with parental smoking habits.

Roughly two-thirds of the tumour samples contained at least one of these deletions, according to the March 22 Cancer Research report.

Deletions were considerably more common in children whose mothers had smoked during pregnancy and after birth. For each five cigarettes smoked daily during pregnancy, there was a 22 percent increase in the number of deletions; and for each five cigarettes smoked daily during breastfeeding, there was a 74 percent increase in the number of deletions.

The smoking of five cigarettes daily by the mother or father before conception also was associated with a seven to eight percent increase in the number of deletions.

Boys were found to be more sensitive to the effects of maternal smoking, including smoking that occurred pre-conception. This could be explained by the fact that male fetuses grow more rapidly, causing increased vulnerability of developing lymphocytes to toxins that cause genetic damage, the authors note.

One limitation of the study is that researchers do not know when genetic deletions occurred relative to the development of leukemia. The researchers also relied on parents to accurately recall and report their smoking habits in questionnaires, making it possible the timing or amount of tobacco exposure might be incorrect in some cases.

Still, the findings should reinforce how important it is for parents to quit or cut back tobacco use, said Oslo University Hospital researcher Marte Reigstad, who was not involved in the study. “The best thing to do to reduce risk to a minimum is to cut out smoking altogether,” Dr Reigstad continued.

The best thing to do to reduce risk to a minimum is to cut out smoking altogether.

For people who grew up with parents that smoked, it is important to understand that tobacco is not the only thing that causes cancer, Dr Reigstad added. “Living healthy lives can also reduce cancer risk, especially concerning exercise and keeping a healthy body weight.”

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