LWBK1006-05 LWW-Govindan-Review November 24, 2011 11:20
Chapter 5•Epidemiology of Cancer 75country with an older or younger population may have a different inci-
dence of a cancer related to the age distribution. Gender similarly influ-
ences the incidence of cancer. A cohort effect typically results from the
introduction of a risk factor that becomes established at a young age in
people born in the same time period. An example would be lung cancer
death rates peaked in cohorts born around the late 1920s and early 1930s,
and cigarette smoking also peaked during this time period.Answer 5.8. The answer is B.
In cohort studies, relative risk is defined as the ratio between cumulative
disease incidence in the exposed group and cumulative disease incidence in
the unexposed group. Absolute risk is calculated as the cumulative inci-
dence in the exposed group minus the cumulative incidence in the unex-
posed group. Relative risk is preferred when the focus of the cohort study
is to infer on the causality of the disease.Answer 5.9. The answer is B.
Genotypic markers are defined as the nucleotide sequences of genomic
DNA, and all other molecules are classified as phenotypic marker. SNPs
are genotypic markers and they do not change with time or due to disease
status. In the case of phenotypic markers such as protein sequence, they
can be affected by the development of disease.Answer 5.10. The answer is E.
Migrant studies have helped to differentiate whether variation in can-
cer rates across countries and among different racial and ethnic groups
is due to environmental factors or inherited factors. In this study, the
increase in the mortality from colorectal cancer among Japanese migrants
was presumably reflecting the changing dietary and physical activity pat-
terns among migrants, and the rate of colorectal cancer in Japan has
increased dramatically since World War II, most likely reflecting changes
in lifestyle in the Japanese population. The higher rate of stomach and
liver cancer among Japanese in Japan and the decline in first-generation
Japanese, and the fact that the risk among second-generation Japanese
and whites is similar most likely reflect the influence of an environmental
exposure.Answer 5.11. The answer is D.
Lead-time bias reflects when earlier detection (lead time) did not change
outcome. For example, a person receives the diagnosis of lung cancer
on screening CT scan in 2008 and subsequently dies of lung cancer in
2010, whereas a person who does not undergo CT screening receives the
diagnosis in 2010 and dies of lung cancer in 2010. The outcome is the
same, but it would appear that the survival time has increased from 1 to
3 years. Length-time bias refers to the detection of indolent cancers by
screening at a higher rate than the more aggressive cancers, resulting in
an apparent survival advantage to screening.