Anthropometry and Multiple Myeloma

To the Editor: The Iowa Women's Health Study, a prospective study including 37,083 postmenopausal women and 95 cases of multiple myeloma (MM), reported that women in the highest category of various anthropometric measures had a 1.5- to 2.0-fold increased risk of MM, suggesting that greater adiposity may increase the risk of developing MM.1 Likewise, in the American Cancer Society Cancer Prevention Study II, the relative risk for obese subjects was around 1.5 for both sexes.2 A few other epidemiologic studies also suggested a modest increase in the risk of MM for subjects with an elevated body mass index (BMI), although the evidence is still limited and inconsistent.1 To further investigate the issue, we analyzed data from a case–control study on lymphoid neoplasms conducted in Italy between 1985 and 1997.3 This included 141 cases of incident, histologically confirmed MM (International Classification of Diseases, 9th revision code 203; 70 men and 71 women) age 38–79 years. Controls were 1112 subjects (530 men and 582 women) age 35–79 years admitted to the same hospitals as cases for a wide range of acute, nonneoplastic conditions not related to tobacco, alcohol, and long-term modifications in diet. Both cases and controls were interviewed in the hospital by trained interviewers using a standard questionnaire. Information was obtained on sociodemographic characteristics, anthropometric measures, tobacco, alcohol and coffee consumption, selected dietary items, a problem-oriented medical history, and selected occupational exposures. Study subjects were asked to report their weight and height 1 year before cancer diagnosis or interview (for controls). BMI, computed as weight/height2, was categorized into 4 levels as defined by the World Health Organization standards, ie, underweight = <18.5 kg/m2, normal weight = 18.5–24.9 kg/m2, overweight = 25.0–29.9 kg/m2, and obese = ≥30.0 kg/m2. Odds ratios (ORs) and corresponding 95% confidence intervals (CIs) were estimated by unconditional logistic regression models, including terms for age, sex, area of residence, education, year at interview, and tobacco smoking. Compared with subjects of normal weight, the ORs were 0.57 (95% CI = 0.15–2.14) for underweight, 1.43 (0.92–2.24) for overweight, and 1.57 for obese subjects (0.81–3.04) (Table). The association with BMI was consistent in the 2 sexes, although somewhat stronger in women (the OR for obese subjects was 1.30 in men and 2.26 in women).TABLE: Distribution of 141 Cases With Multiple Myeloma, and 1112 Controls, With Corresponding Odds Ratios and 95% Confidence Intervals, According to Body Mass Index, Italy, 1985–1997Although our study could have some of the limitations of hospital-based case–control studies, these should be limited given the exclusion of controls with chronic conditions potentially related to lifestyle factors, the administration of a standard questionnaire to both cases and controls under similar conditions, the same catchment area for cases and controls, and their almost complete participation. Self-reported weight and height are typically highly correlated with actual measurements, and there is no reason to suggest differential reporting by cases and controls. Furthermore, adjustment was made for potentially relevant confounding variables. The present data provide further support to the hypothesis that obesity may be related to a modest increased risk of MM. It has been suggested that obesity may affect immunologic responses that are involved in the development of MM.4,5 One alternative explanation of the association between obesity and MM risk is increased insulin resistance and consequent increased insulin-like growth factor production, which is in turn involved in the process of mitogenesis and carcinogenesis; another possible mechanism involves IL-6, produced in the bone marrow but also synthesized in adipose tissue, and involved in the proliferation and differentiation of plasma cells.6–8 However, the biologic mechanisms need to be further clarified. Cristina Bosetti Laboratorio di Epidemiologia Istituto di Ricerche Farmacologiche “Mario Negri” Milan, Italy [email protected] Eva Negri Silvano Gallus Istituto di Ricerche Farmacologiche “Mario Negri” Milan, Italy Luigino Dal Maso Servizio di Epidemiologia e Biostatistica Centro di Riferimento Oncologico Aviano (PN), Italy Silvia Franceschi International Agency for Research on Cancer Lyon, France Carlo La Vecchia Istituto di Ricerche Farmacologiche “Mario Negri” Istituto di Statistica Medica e Biometria Università degli Studi di Milano Milan, Italy