Family history of haematopoietic malignancies appears to be a risk factor for non-Hodgkin's lymphoma (NHL), but whether risk varies by family member's gender is unclear. Among 121 216 women participating in the prospective California Teachers Study, NHL risk varied by type of haematopoietic malignancy and gender of the relative. Evidence from epidemiologic studies shows that the risk of nonHodgkin's lymphoma (NHL) is increased by approximately twofold for individuals with a first-degree family history (parent, sibling or child) of haematopoietic malignancy (Pottern et al, 1991;Zhu et al, 1998;Chiu et al, 2004;Altieri et al, 2005;Chang et al, 2005;Goldin et al, 2005;Wang et al, 2007). However, the underlying mechanisms are poorly understood.A recent analysis from the International Lymphoma Epidemiology (InterLymph) Consortium of NHL case -control studies found an increased risk of NHL for individuals who reported having a first-degree relative with a haematopoietic malignancy (NHL, Hodgkin's lymphoma, leukaemia or multiple myeloma) (Wang et al, 2007). They also found that NHL risk differed by the gender and familial relationship of the affected relative. These findings were based on case -control studies using retrospectively self-reported data on family history, and were therefore potentially subject to survival bias and differential recall bias (Chang et al, 2006). To understand the underlying disease mechanisms in NHL better, we used data from the prospective California Teachers Study to investigate NHL risks associated with first-degree family history.
MATERIALS AND METHODSA detailed description of the California Teachers Study has been published elsewhere (Bernstein et al, 2002). In this analysis, we included 121 216 women who were California residents, were under the age of 85 years at baseline and had no prior history of a haematopoietic malignancy. Use of human subjects in this study was approved by each participating institution.Incident diagnoses of B-cell NHL (International Classification of Diseases for Oncology third edition morphology codes: 9590, 9591, 9670 -9675, 9680 -9699, 9727, 9823, 9832, 9835 and 9836) were identified through annual linkages with the population-based California Cancer Registry. Person-time was accrued from the date a participant completed her baseline questionnaire until the first occurrence of either a diagnosis of a B-cell NHL or a censoring event: a move outside of California; a first diagnosis of another haematopoietic malignancy not included in our case definition; death; or 31 December 2005.The self-administered, baseline questionnaire collected detailed information on personal and family history of cancer. Having 'no family history' of a haematopoietic malignancy was defined as reporting no first-degree relative with NHL, Hodgkin's lymphoma or leukaemia.We used Cox proportional hazards regression models, stratified by age in years at baseline, to estimate hazard rate ratios (RR) and 95% confidence intervals (CIs) for B-cell NHL, using age in days from baseline until ...