Interleukin-6-related genotypes, body mass index, and risk of multiple myeloma and plasmacytoma.

Interleukin-6 (IL-6) promotes normal plasma cell development and proliferation of myeloma cells in culture. We evaluated IL-6 genotypes and body mass index (BMI) in a case-control study of multiple myeloma and plasmacytoma. DNA samples and questionnaires were obtained from incident cases of multiple myeloma (n = 134) and plasmacytoma (n = 16; plasma cell neoplasms) ascertained from the Los Angeles County population-based cancer registry and from siblings or cousins of cases (family controls, n = 112) and population controls (n = 126). Genotypes evaluated included IL-6 promoter gene single nucleotide polymorphisms (SNP) at positions -174, -572, and -597; one variable number of tandem repeats (-373 A(n)T(n)); and one SNP in the IL-6 receptor (IL-6ralpha) gene at position -358. The variant allele of the IL-6 promoter SNP -572 was associated with a roughly 2-fold increased risk of plasma cell neoplasms when cases were compared with family odds ratio (OR), 1.8; 95% confidence interval (95% CI), 0.7-4.7] or population controls (OR, 2.4; 95% CI, 1.2-4.7). The -373 9A/9A genotype was associated with a decreased risk compared with the most common genotype (OR for cases versus family controls, 0.4; 95% CI, 0.1-1.7; OR for cases versus population controls, 0.3; 95% CI, 0.1-0.9). No other SNPs were associated with risk. Obesity (BMI >or= 30 kg/m(2)) increased risk nonsignificantly by 40% and 80% when cases were compared with family controls or population controls, respectively, relative to persons with a BMI of <25 kg/m(2). These results suggest that IL-6 promoter genotypes may be associated with increased risk of plasma cell neoplasms.