A recently published study from investigators at Stanford University and in Lund University in Sweden used data from a large Swedish cohort study, birth records, and cancer registries to look for risk factors associated with development of non-Hodgkin lymphoma (NHL). The investigators evaluated the records of over 3.5 million people, including 936 with NHL, born between 1973 and 2008.
They reported that family history of NHL was associated with development of NHL in early life. Specifically, history of NHL in a sibling increased the risk of developing NHL roughly nine-fold while having a parent with NHL increased the risk of NHL roughly two-fold. Importantly, the overall incidence rate of NHL was 1.4 per 100,000 person-years (the number of people x the number of years of follow-up per person). Therefore, a two-fold increase, although statistically significant, would only have increased the rate to roughly 3 per 100,000 person years. Moreover, only 4 of the 936 cases had a sibling with NHL and 10 had a parent with NHL.
These small numbers, although statistically significant, make it difficult to make any definitive conclusions regarding the degree of risk. The lack of data regarding environmental exposures, infections, and other co-existing conditions (e.g., immunodeficiencies) make it difficult to determine whether the familial association of NHL is due to an inherited condition or some other unmeasured factor. Despite the issues, the results are consistent with the concept that genetic factors may contribute to NHL. It is possible that contemporary studies using next generation sequencing of the genomes of patients and family members could yield more conclusive results. The risks and benefits of such studies, however, need to be weighed very carefully.