Multiple myeloma (MM) and monoclonal gammopathy of undetermined significance (MGUS), a precursor to MM, are 2 to 3 times more common in African Americans than European Americans, representing one of the largest racial disparities of all cancer types. According to the results of a study published in Blood Cancer Journal, the increased incidence of MM among people of African descent is driven specifically by the higher frequency of 3 cytogenetic subtypes: t(11;14), t(14;16), and t(14;20).1
The study included 881 samples from patients with monoclonal gammopathy, the majority of whom had been diagnosed with MM. About half the patients were treated at the Mayo Clinic in Minnesota, Florida, or Arizona, and half were seen at other hospitals in the United States.
Although there has been previous research looking at the racial disparity in MM subtypes, the current study is the first to conduct ancestry analysis, which was based on single-nucleotide polymorphism (SNP) array, said S. Vincent Rajkumar, MD, professor of medicine at Mayo Clinic in Minnesota, who led the study. Earlier studies relied on self-reports of race, which may be inaccurate. In addition, there was a high degree of admixture, and the ancestry analysis allowed the researchers to determine the proportion of genes among the patients that were associated with different ancestries, he said.
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The research team analyzed the samples using fluorescence in situ hybridization (FISH) to probe for chromosomal translocations, hyperdiploidy, deletions, and other common cytogenetic abnormalities that are normally present in MM. “There are many types of myeloma and it’s very unlikely that the frequency of all types would increase in a particular race; that would be like lightning striking twice,” Dr Rajkumar said.
The researchers found that the likelihood of having t(11;14), t(14;16), and t(14;20) subtypes increased with every 10% increase in the extent of African ancestry. Among the 881 patients studied, the discrepancy was most pronounced when comparing the 120 individuals who had more than 80% African ancestry with the 235 individuals who had less than 0.1% African ancestry.
Among the individuals of African descent with 1 of these 3 subtypes, t(11;14) was the most common, accounting for 75% of these cases. The t(11;14) subtype has a favorable prognosis compared with other subtypes, whereas t(14;16) and t(14;20) are considered high-risk, but are much rarer. The overrepresentation of t(11;14) subtype among individuals of African descent could help explain why African Americans have been reported to have better survival outcomes compared with European Americans, Dr Rajkumar said.
