Background: It has been suggested that certain medical conditions and drug exposures might suppress the immune system and increase the risk of developing non-Hodgkin's lymphoma (NHL).
Purpose: We investigated whether specific medical conditions and drug exposures were associated with the risk of NHL in a cohort of older women who were enrolled in the Iowa Women's Health Study.
Methods: A cohort of 41837 women, 55-69 years of age at baseline, was followed prospectively for the development of cancer from 1986 through 1992. These women had completed a baseline questionnaire in January 1986 that inquired about the occurrence and age at onset of specific medical conditions, about family history of cancer, and about the use of selected medications. Follow-up questionnaires were mailed to the women in 1987, 1989, and 1992. Incident cancers and deaths were ascertained through linkages to state and national databases. For most analyses, women with a self-reported history of cancer at baseline (n = 3903) were excluded. Relative risks (RRs) and 95% confidence intervals (CIs), adjusted for age or for age and other variables, were used as a measure of the association between NHL and medical history factors. Reported P values are two-sided.
Results: One hundred fourteen incident cases of NHL were identified in the cohort during follow-up. A history of adult-onset diabetes mellitus (i.e., first diagnosed after the age of 30 years) was associated with an increased risk of developing NHL (age-adjusted RR = 2.18; 95% CI = 1.22-3.90). In addition, there was an association between the duration of adult-onset diabetes and increasing risk of NHL (P for trend = .004), with an age-adjusted RR of 2.90 (95% CI = 1.07-7.90) for women with a diagnosis of diabetes for 15 or more years compared with women with no diagnosis of diabetes. Women with a history of blood transfusion were also at increased risk for the development of NHL (age-adjusted RR = 1.95; 95% CI = 1.33-2.85). The risk estimates for diabetes and transfusion history were independent of each other and were not changed substantially after adjustment for other risk factors. History of a previous cancer (excluding hematopoietic and lymphatic cancers) was associated with an increased risk of NHL (age-adjusted RR = 1.92; 95% CI = 1.21-3.06); this risk estimate was attenuated somewhat after adjustment for a history of diabetes, transfusion history, and other major risk factors (RR = 1.66; 95% CI = 1.02-2.69). No statistically significant associations were found between NHL and a history of chronic colitis, nonestrogen steroid use, use of exogenous estrogens, or use of thyroid medications.
Conclusions and implications: A history of adult-onset diabetes mellitus, blood transfusion, and a history of cancer (or its treatment) appear to be independent risk factors for NHL in older women.