Children whose fathers smoked have at least a 15 percent higher risk of developing the most common form of childhood cancer, a new Australian study finds.

“Paternal smoking seems to be real” as a risk factor, said Patricia Buffler, a professor at the University of California, Berkeley, who was not involved in the current analysis.

“The importance of tobacco exposure and children’s cancers has been overlooked until recently,” Buffler told Reuters Health. “So I think this paper is important” in adding to the growing body of evidence.

The research team, led by Dr. Elizabeth Milne at the Telethon Institute for Child Health Research in Australia, surveyed the families of nearly 400 children with acute lymphoblastic leukemia (ALL).

Although ALL is the most common childhood cancer, it is still rare, affecting about three to five children out of every 100,000, according to the National Cancer Institute. More than 1,000 kids die of the disease every year.