Background: Endogenous sex hormones, particularly estrogens, modulate the immune system, and non-Hodgkin lymphoma (NHL) is a tumor that is related to immunologic status.
Methods: Self-reported menstrual and reproductive history and risk of NHL were evaluated in a cohort of 37,934 Iowa women who were aged 55-69 years when first enrolled in 1986. Through 1998, 261 cases of NHL were identified by linkage to the Iowa SEER Cancer Registry.
Results: After multivariate adjustment there was no association between NHL incidence and age at menarche, age at menopause, type of menopause, history of infertility, number of miscarriages, or history of induced abortion, while there were suggestive inverse associations with nulliparity (RR=0.65; 95% CI 0.36-1.16) and years of ovulation (RR = 0.76 for >37 compared to <28 ovulatory years: p-trend = 0.07). Among parous women there was no association with number of livebirths or age at first livebirth, but there was an inverse association with number of children who were breast-fed (RR=0.52 for breast-feeding >2 children versus none; 95% CI 0.33-0.82).
Conclusions: Overall, menstrual and reproductive factors were not strongly related to NHL incidence. The inverse association with breast-feeding is novel but requires confirmation in other studies.