Distribution of Cytogenetic Abnormalities in African American Multiple Myeloma Patients May be Unique for Different Geographic Regions

BACKGROUND: Multiple myeloma (MM) is the most common hematologic malignancy in the African American population, with an incidence more than 2 times higher than Caucasian population [Landgren O et al Blood 2006]. Historically, the African American MM patients have had better outcomes compared with other races [Ailawadhi S et al Br J Haematol 2012], but no biologic explanations exist for this observation. Greenberg et al [Blood Cancer J 2015] have recently reported on differences in commonly observed baseline cytogenetic abnormalities (CA) between African American and Caucasian MM patients seen at Mayo Clinic (Rochester, MN), Cook County Hospital (Chicago, IL) and University of Maryland (Baltimore, MD). We examined the MM cohort at our referral center to validate these observations.

PATIENTS & METHODS: The Levine Cancer Institute MM database was interrogated for all patients presenting with MM between January 2012 and April 2015. Baseline clinical and pathology variables were compared between the African American and Caucasian cohorts. Continuous variables were compared using nonparametric rank tests, while incidences and proportions (e.g. CAs including t(11;14), t(4;14), monosomy13/del13q and del17p) were compared using Fisher's exact tests.

RESULTS: A total of 662 patients were identified; excluding those with MGUS classification, 368 patients were included in the analysis (African Americans n = 130, Caucasian n = 238). The median age of African American MM patients was significantly younger than Caucasian MM patients (median age 60 years vs. 65 years, p=0.010), with similar gender distribution. There was a numerically larger proportion of African American patients with anemia (40.8% vs 30.8%, p =0.166), however, there was no significant difference in degree of BM plasmacytosis amongst the two groups. The overall distribution of MM patients by IMWG risk stratification (Chng et al, Leukemia 2013) was also similar between the two groups. The African American MM patients had a numerically higher incidence of a metaphase abnormality on conventional cytogenetics (21.7% vs. 13.9%, p =0.154). They had a significantly lower incidence of t(11;14) [7.7% vs. 16%, p=0.024], a numerically higher incidence of t(4;14) [6.2% vs. 3.8%, p=0.309], and similar incidence of deletion 13/del13q [22.3% vs. 18.9%, p=NS ] and del17p [7.7% vs. 7.6%, p=NS ].

CONCLUSIONS: The present dataset is the largest single institution report on CA racial differences in MM patients. We found that unlike previous reports of lower incidence of t(4;14) or del17 p in African American MM patients by Greenberg et al, we have observed a higher incidence of t(4;14) and similar incidence of del17p in our experience compared to Caucasian MM patients. The different pattern of CA distribution compared to published literature may represent geographic heterogeneity and potentially influence survival outcomes.