Epidemiology and Clinical Outcomes of the M-Component Immunoglobulin Types of Multiple Myeloma in an Inner City Hispanic Population.

Introduction: Different types of myeloma are classified by the type of immunoglobulin. From prior analysis, we know that IgG is the commonest class of myeloma and that this type seems to be the most benign. While IgA myeloma appear to be of intermediate outcome, IgD myeloma and lambda light-chain disease are the most aggressive types. Breakdown by immunoglobulin type reveals higher prevalence of IgG myeloma among Whites, compared to Blacks. This study examines the type of immunoglobulin and clinical implication in Hispanics compared to other ethnic groups.

Methods: In a single inner city institution, we retrospectively examined patients diagnosed with multiple myeloma over a 5-year period. This investigation defined Hispanic patients as those of Latin American descent. We identified the M-component immunoglobulin type from immunoelectrophoresis as reported in medical records. New onset renal failure and disease related mortality are considered as adverse clinical outcomes. Various ethnic groups were compared between the type of immunoglobulin and adverse clinical outcomes using chi-square test.

Results: A total of 203 patients were examined, of which 63 (30.9%) were Hispanics, 87 (42.9%) Caucasians and 53 (26.2%) African American, (104 males, 99 females, age range 34 – 93 yrs, mean age 67.45 ± sd 10.28 yrs). IgG and IgA M-components predominated among all ethnic groups respectively Hispanics 36 (57.9%), 6 (10.5%), Caucasians 51 (59%), 18 (22.7%) and African Americans 25 (50%), 20 (37.5%). A higher proportion of light-chain cases were seen among Hispanics since 21 (31.6%) had no peak on immunoelectrophoresis compared to Caucasians 31 (18.3%) and African Americans 8 (12.5%) (chi-square test, two-tailed p=0.426). Adverse clinical outcomes of new onset renal failure developed correspondingly in 20 (31.6%) Hispanics, 31 (36.3%) Caucasians and 15 (28.6%) African Americans while disease related mortality occurred in 20 (31.6%) Hispanics, 18 (21.4%) Caucasians and 9 (18.2%) African Americans (chi-square test, two-tailed p= 0.132). However, differences were not statistically significant.

Conclusion: Although Hispanics exhibited more myeloma of light chain type and worse clinical outcomes compared to other ethnic groups, our study was unable to detect a statistical disparity. Further prospective large population based studies via the new light chain immunodiagnostic assay are warranted to define the epidemiology of this disease.