Reproductive patterns and non-Hodgkin lymphoma risk in Danish women and men

Reproductive patterns have been inconsistently linked to risk of non-Hodgkin lymphoma (NHL) in women, and fathering patterns in relation to NHL risk have not been studied. The authors conducted a register-based cohort study of 4.1 million Danes to investigate associations of livebirths with subsequent NHL incidence (85 million person-years, 3819 NHL cases). The impact of induced abortions, ectopic pregnancies, spontaneous abortions, missed abortions, stillbirths, and hydatidiform moles on subsequent NHL incidence was studied in a subcohort of 1.2 million women. Ratios of NHL incidence rates, accompanying trend tests and two-sided p-values were calculated by log-linear Poisson regression analyses. Pregnancies, whether ending in livebirths or not, were unrelated to NHL incidence in women. The only statistically significant finding in women was that, among parous women, age at first child-birth was inversely associated with NHL incidence (p-trend = 0.001). In men, there was no overall difference in NHL incidence between fathers and non-fathers. However, in men with children, NHL risk declined with increasing number of children (p-trend = 0.02) and increased with time since birth of the most recent child (p-trend < 0.001). Pregnancies have limited impact, if any, on subsequent NHL risk in women. Our findings in men need replication, but, if verified, they may reflect lymphomagenesis-associated male subfertility prior to NHL diagnosis.