A new study has linked a father’s age at his child’s birth to the risk that the child will develop a hematologic malignancy as an adult, but this risk only proved significant among children without siblings.
Only-children whose fathers were 35 or older at the child’s birth were significantly more likely to develop hematologic malignancies than only-children with fathers who were younger than 25 at the child’s birth.
There was no association between these cancers and a mother’s age, either among only-children or those with siblings.
A previous study of more than 100,000 women also showed an association between paternal—but not maternal—age at a child’s birth and the risk of hematologic malignancy.
To further investigate the association, Lauren Teras, PhD, of the American Cancer Society in Atlanta, Georgia, and her colleagues analyzed data from women and men enrolled in the American Cancer Society Cancer Prevention Study-II Nutrition Cohort.
The team reported their findings in the American Journal of Epidemiology.
Among the 138,003 participants, there were 2532 cases of hematologic malignancies diagnosed between 1992 and 2009.
Subjects’ mothers tended to be younger at their birth than fathers, with median ages of 27 and 31, respectively. Almost a third of the fathers were 35 or older when a subject was born, compared with 17% of the mothers.
In the categorical analysis, the researchers found a positive association between older paternal age at a subject’s birth and the risk of hematologic malignancies in male, but not female, subjects. The hazard ratio (HR) was 1.35 for male subjects with fathers aged 35 and older compared to those whose fathers were younger than 25.
On the other hand, when paternal age was modeled as a continuous variable, there was no association with the risk of hematologic malignancy for males or females. Likewise, there was no association between maternal age at a subject’s birth and the risk of hematologic malignancy in male or female subjects.
However, among subjects without siblings, there was a significant, positive association with paternal age and the risk of hematologic malignancy (P=0.002).
When the researchers separated only-children by sex, they found a suggestive positive association between paternal age and hematologic malignancy for females (HR=1.40) and a significant association for males (HR=1.84). However, the linear spline was significant for males (P=0.01) and females (P=0.04).
There was no association between paternal age at a subject’s birth and the risk of hematologic malignancy among subjects with at least 1 sibling (HR=1.06).
The researchers said the fact that the association between paternal age and malignancy was significant in subjects with no siblings suggests it may be related to the “hygiene hypothesis”—the idea that exposure to mild infections in childhood, which might be more numerous with more siblings, are important to immune system development and may reduce the risk of immune-related diseases.
It is possible that the combination of having an older father and no siblings may promote cell proliferation in those individuals with an underdeveloped immune system and, as such, favors the development of cancers related to the immune system, the team said.
They added that this study suggests a need for further research to better understand the association between paternal age at a child’s birth and hematologic malignancies.
“The lifetime risk of these cancers is fairly low—about 1 in 20 men and women will be diagnosed with lymphoma, leukemia, or myeloma at some point during their lifetime—so people born to older fathers should not be alarmed,” Dr Teras said.
“Still, the study does highlight the need for more research to confirm these findings and to clarify the biologic underpinning for this association, given the growing number of children born to older fathers in the United States and worldwide.”
