Findings from a recent analysis conducted in the United States indicate that African-American multiple myeloma patients may have a lower frequency of certain chromosomal abnormalities compared to European-American patients.

In particular, the investigators from the Mayo Clinic found that African-Americans with myeloma may have a lower rate of chromosome 14 trans­locations.

Chromosome 14 translocations are typically associated with myeloma that is more aggressive and harder-to-treat.

The Mayo researchers note that, although their results suggest that African-Americans may have myeloma which, on average, is less aggressive than myeloma in European-Americans, there are many other genetic differences between the two patient groups that were not accounted for in the study.

However, the researchers still believe their findings may help explain differences in treatment outcomes that have been observed between the two patient groups.

Previous studies have shown that African-Americans are diagnosed with multiple myeloma two to three times more frequently than European-Americans.

However, African-American myeloma patients also have higher survival rates.

Previous studies also have shown that African-Americans with the myeloma precursor disease monoclonal gammopathy of undetermined significance (MGUS) have lower levels of monoclonal (M) protein, and an earlier age of onset, compared to European-Americans.

MGUS is a plasma cell disorder characterized by elevated levels of M-protein in the blood. However, unlike myeloma patients, MGUS patients do not experience any disease-related symptoms and typically do not receive treatment unless their condition worsens.

According to the study authors, no previous study has directly compared and characterized the genetic differences between African-American and European-American myeloma patients, despite the observed clinical differences between the two groups.

Therefore, the researchers compared the genetic makeup of 115 African-American patients with that of 353 European-American patients, with the aim of understanding the clinical differences in myeloma in each group.

The investigators found that fewer African-American patients had chromosome 14 translocations, which researchers often describe as "IgH translocations."

Among African-American myeloma patients, chromosome 14 translocations were found in 40 percent of the patients.  In European-American patients, such abnormalities were found 52 percent of the time.

There were not, however, statistically significant differences in how often common chromosome 14 translocations – t(4;14), t(11;14), and t(14;16) – occurred in the two patient groups.

In fact, African-American myeloma patients were more likely to have the t(11;14) and t(14;16) abnormalities than European-American patients. The differences in how often these two abnormalities occurred were not, however, statistically significant.

The researchers also studied the prevalence of two specific subsets of myeloma, hyperdiploid and nonhyperdiploid myeloma, in two smaller samples of African-American and European-American patients (45 and 196 patients, respectively).

Patients with hyperdiploid myeloma have between 48 to 74 chromosomes (more than the normal 46 chromosomes), while patients with nonhyperdiploid myeloma have either lower than 48 or greater than 74 chromosomes.

Previous studies have shown that patients with hyperdiploid myeloma may have better overall survival than patients with nonhyperdiploid myeloma.

In the current study, the investigators found that African-American and European–American myeloma patients had similar rates of both hyperdiploid myeloma (53 percent for both groups) and nonhyperdiploid myeloma (47 percent and 48 percent, respectively).  The researchers point out that these results are similar to those reported in previous studies.

Finally, the researchers used a technique known as gene expression profiling to analyze data for two additional samples of myeloma patients (35 African-Americans, and 178 European-Americans).

Using this technique, they found that there was no statistically significant difference in the share of patients in the two groups that had a genetic profile associated with high-risk (poorer prognosis) disease.

Among the African-American patients, 31 percent had a high-risk gene expression profile.  Among the European-American patients, 34 percent had such a profile.

Thus, the different analyses the investigators carried out did find one potential explanation – a lower rate of chromosome 14 translocations – for the comparatively better prognosis African-American myeloma patients have compared to European-American patients.

However, the authors acknowledge that other factors which they were not able to identify with their analyses also may account for the observed clinical differences between the two patient groups.

For more information, please refer to the study in the journal Blood (abstract).