Cancer incidence and mortality rates vary among ethnic
and racial groups. These differences offer clues to the causes, risk factors,
and forces that influence the development and progression of cancer. Although
some authors have attributed varying rates to genetic differences, epigenetic
influences on cancer are becoming more appreciated. Still, as cancer research
seeks to explain why cancer statistics differ among various groups of people,
practical details concerning research on racial and ethnic groups remain
Two questions are critical: (1) When is genetic research on a population
appropriate? (2) How should researchers define a given population being studied?
All research on ethnic groups must, in fact, address these two questions, even
if investigators do not explicitly take them into consideration. Studies of
Ashkenazi Jews and BRCA1/2, for instance, represent fairly concrete genetic
analyses on a specific population. As such, an examination of these studies
offers a simplified vantage point from which to dissect the practicalities of
ethnic research as well as clarify what is necessary for research concerning all
racial and ethnic groups.
The concept of "race" implies a genetic homogeneity among a group
of people that correlates with skin hue or other physical characteristics. Yet
modern genetic techniques have repeatedly demonstrated that the amount of
variation within a racial group is greater than the difference between two
groups. Such findings are not surprising, given the arbitrary nature of
definitions used to categorize people. For instance, in Virginia in 1750, a
person was considered a member of the "Negro" race if born to a
"Negro" mother. Later, the definition was changed, and a person was
designated as Negro if he or she had "one drop of Negro blood."
Moreover, at varying times in the 20th century, immigrants from India have been
categorized as white, Asian, and Indian. Clearly then, such definitions are
political and unscientific. Dividing people into racial groups is more a
consequence of social constructs than a reflection of biological reality.
"Ethnicity" is another term that is sometimes used interchangeably
with "race." Yet, unlike race, ethnicity includes a variety of social
factors and is not strictly a biological term. As Bhopal defines it,
ethnicity denotes "a group that people belong to because of shared
characteristics, including ancestral and geographical origins, cultural
traditions, and language." Like race, however, ethnicity is a socially
constructed phenomenon. Ethnic boundaries are based primarily on
self-assessment, and are thus inherently imprecise and can change over time or
depending on the specific context.
Thus, it is not surprising that racial and ethnic groups do not represent a
genetically homogeneous population. In some instances, however, a correlation
exists between an ethnic group and a specific mutation, as can occur in
situations of enforced segregation. For example, approximately 20% of Ashkenazi
Jewish women with breast cancer carry mutations in BRCA1 or BRCA2a finding
that is 10- to 15-fold higher than in breast cancer patients who are not
Jewish. Specific mutations in both BRCA1 and BRCA2 are present at least 10
times more often in unaffected Ashkenazi Jewish women than in the general
population. Nevertheless, the Ashkenazi Jewish population does not monopolize
the gene. The genetic mutations associated with cancer have been found in people
of several races and ethnicities.
Familial vs Racial Correlations
Although they have been associated with the entire Ashkenazi population, such
genetic abnormalities should be considered familial and not racial. This is
particularly true given the high rates of intermarriage among the American
Jewish population; any genetic homogeneity that may have existed under the
conditions of segregated ghettos in Eastern Europe has been and continues to be
diluted. This point is confirmed by looking at the prevalence of the 185delAG
BRCA1 mutation among groups of Ashkenazi Jewish breast cancer patients, as was
determined in 14 separate studies.
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