Parents’ smoking habits could contribute to the most common form of childhood cancer, according to a new study.
A new study by researchers in California suggests exposure to parents’ tobacco smoke, especially during pregnancy and early childhood, may be linked to gene changes commonly found in acute lymphoblastic leukemia (ALL).
Acute lymphoblastic leukemia is a blood cancer that occurs when bone marrow produces irregular lymphocytes, or new white blood cells, with DNA mutations called deletions. These cancerous cells spread rapidly, overtaking healthy blood cells.
Researchers compared the tumor cells of children exposed to tobacco smoke with those of children not exposed to examine the effects of smoke on cancer risk.
“By examining genetic changes in the leukemia cells of children exposed to tobacco smoke in early life and comparing those with the changes found in leukemia cells of unexposed children, we might find clues to explain the role of tobacco smoke in childhood leukemia development,” said lead study author Adam De Smith in an email.
Previous studies have linked tobacco smoke with adult cancer and also linked childhood cancer with fathers who smoke. But those studies produced inconsistent results for maternal smoking and relied on interview data, said De Smith, a researcher at the Helen Diller Family Comprehensive Cancer Center, University of California, San Francisco.
For this study, researchers compared pretreatment tumor cells of 599 patients, looking for common gene deletions and whether any were associated with parental smoking, according to Reuters.
About two-thirds of the samples contained the gene deletions, which were significantly more common in children whose mothers smoked during pregnancy and after.
“Our study is important because it is the first to report a link between parental smoking and a specific genetic change in childhood ALL, as we found that tobacco smoke exposure was associated with the number of gene deletions in the child’s leukemia cells,” De Smith said.
More than 5,400 children were expected to develop leukemia in 2016, according to the Leukemia and Lymphoma Society. Acute lymphoblastic leukemia accounts for about 75 percent of leukemia cases and is most common between ages 2 and 5.
Survival rates for ALL have increased significantly in recent decades, rising to about 91 percent for children under 15 and 93 percent for children under 5. By discovering the causes of leukemia, scientists may eventually be able to prevent it, De Smith said.
“Part of our research is focused on identifying risk factors for childhood leukemia, in the hope that by reducing or removing these from the environment we may be able to one day prevent disease,” said De Smith.
In the cases De Smith and his team studied, for every five cigarettes a mother smoked while pregnant, the number of gene deletions increased 22 percent, Reuters reported. For every five a mother smoked while breastfeeding, the number of deletions increased 74 percent.
Smoking can even increase risk before conception, though not as seriously as prenatal smoking or smoking after birth, Reuters reported. For every five cigarettes smoked by either parent before conception, the number of deletions increased about 8 percent. The deletions were also more common in boys whose mothers smoked.
But cancer experts cautioned that the study, while suggestive, is not conclusive.
“The authors report a mechanistic study that sheds new light on one of the ways that smoking could influence the risk for childhood leukemia,” said Dr. Stephen Chanock, director of Cancer Epidemiology and Genetics for the National Cancer Institute.
“It is an innovative discovery that will need to be replicated in a separate study and pursued in parallel studies to understand how and why smoking during or shortly after birth could contribute to specific types of leukemia,” he added.
Two out of five children are exposed to secondhand smoke, according to the Centers for Disease Control and Prevention. Exposure is higher among children between 3 and 11 years, black children, and those who live in rental housing or live below the poverty line, according to the CDC.