Mayo Clinic researchers have found that the incidence of a rare and deadly tumour called primary central nervous system lymphoma (PCNSL) is two times higher in black Americans than their white counterparts.
Writing in the Journal of Neuro-Oncology, the researchers have revealed that this finding applies to people aged 20 to 49.
In patients older than 49, according to them, the results were reversed: white Americans were twice as likely as black Americans to be diagnosed with PCNSL.
It most often affects the elderly, people who are immunosuppressed because of illness or transplant, and patients with AIDS.
Though uncommon, PCNSL is increasing in incidence, even in patients without known risk factors.
"We undertook this epidemiological study to look for clues about the cause of PCNSL," says Dr. Brian O'Neill, a Mayo Clinic neurologist and the senior researcher in the study.
The study was conducted by reviewing the records of 2,665 patients between 1992 and 2002 in 13 U.S. communities that are part of the Surveillance, Epidemiology, and End Results (SEER) Program of the National Cancer Institute.
This program is a repository for population-based information on cancer incidence and survival, covering 26 percent of the population and balanced for geographic, race and age differences. It has been used for etiologic cancer research for more than 30 years.
According to the researchers, the number of American Indians, Alaska Natives and Asian/Pacific Islanders diagnosed with PCNSL was too low to draw any conclusions about disease incidence.
In this study, the 12-month survival rate for white Americans was 34 percent, compared to 19 percent among black Americans. Though the difference between the races narrowed over time, the mortality rate continued to be better for white Americans.
At the five-year mark, 16 percent of white Americans were alive, compared to only 9 percent of black Americans.
This is the first time that any study has quantified incidence of PCNSL by racial groups.
The researchers say that they have yet to identify reasons for the racial differences, and why they changed with age.
"We don't know if it's genetic, environmental or a combination. We don't know if the higher incidence in younger black Americans reflects socio-economic factors, access to health care, and also the role of HIV infection in black communities," says Dr. O'Neill.