Reproductive factors and risk of intermediate- or high-grade B-Cell non-Hodgkin's lymphoma in women.

PURPOSE: The incidence rates of non-Hodgkin's lymphoma (NHL) unrelated to human immunodeficiency virus infection are lower for women than for men; yet, few factors have been identified that may account for this difference in risk. NHL is difficult to study epidemiologically because this disorder represents a group of malignancies that differ in terms of morphologic presentation, immunologic features, genetic characteristics, prognosis, and etiology. PATIENTS AND METHODS: We conducted a population-based case-control study in women to determine whether reproductive factors or hormonal exposures might be related to the risk of high- or intermediate-grade B-cell NHL. We interviewed 177 female residents of Los Angeles County who were diagnosed with high- or intermediate-grade B-cell NHL between 1989 and 1992; each case patient was individually matched on age and race to a control subject who lived in her neighborhood. RESULTS: Women who had used oral contraceptives had significantly lower risk of intermediate- or high-grade NHL (multivariate odds ratio [OR] = 0.47; 95% confidence interval [CI], 0.26 to 0.86) than women who had never used these compounds. Among parous women, those who had used lactation suppressants (which contain high levels of estrogen) had significantly lower risk of NHL (multivariate OR = 0.50; 95% CI, 0.29 to 0.85) than unexposed women. Postmenopausal women had a somewhat greater risk of NHL than premenopausal women, whereas those postmenopausal women who had used hormone replacement therapy (HRT) (primarily estrogen) had somewhat lower risk than those who had not used HRT. CONCLUSION: Exogenous estrogens seem to have a protective effect on the risk of high- and intermediate-grade B-cell NHL. Although the mechanisms for such protection are not known, alterations in immune reactivity, cytokine expression, or B-cell modulation may play a role.