Multiple myeloma is one of the most common blood-related diseases among African Americans. After lymphoma and leukemia, it is the third-most-common blood cancer. Multiple myeloma occurs twice as often among African Americans as it does among Caucasians, especially as age increases. This may be because Caucasian patients tend to respond to treatments for multiple myeloma whereas African American patients often do not. Multiple myeloma is also more common in North Africa, the Middle East, and the Mediterranean. Asian Americans are least likely to develop this type of cancer. Researchers have not yet discovered why race is a risk factor for developing multiple myeloma.