Tobacco and Public Health - TCSC Indonesia

Introduction
Chapter 25
Cigarette smoking and
colorectal cancer
Edward Giovannucci
Our understanding of the potential association between tobacco and risk of colorectal
cancer has had an interesting history. The landmark early studies, which covered the
1950s and 1960s, consistently did not support an association between tobacco and
colorectal cancer risk (Hammond and Horn 1958, 1966; Higginson 1966; Kahn 1966;
Staszewski 1969; Weir and Dunn 1970; Doll and Peto 1976; Williams and Horm 1977;
Graham et al. 1978; Doll et al. 1980; Haenszel et al. 1980; Rogot and Murray 1980).
Many of these studies had been instrumental in demonstrating important associations
with other cancer sites. Generally, by the 1970s, tobacco was not considered an important
risk factor for colorectal cancer. However, around this time colorectal adenomas
had become established as cancer precursors through careful pathologic studies
(Morson 1974; Lev 1990). Epidemiologists began studying risk factors for colorectal
adenomas in studies conducted in the 1980s and 1990s, and smokers were consistently
found to have an appreciably elevated risk. In 1994, a hypothesis, attempting to reconcile
the apparent paradox findings between colorectal adenomas and cancers, stated
that carcinogens from cigarette smoke cause irreversible genetic damage in colorectal
epithelial cells, but several decades are required for completion of all the carcinogenic
events following this initiating event (Giovannucci et al. 1994a, b). This hypothesis
predicted that an association would be observed initially in adenomas, and then in
cancers, after a certain period of time. Thus, the early studies may not have considered
a sufficiently long time lag between smoking exposure and time of risk, and thus may
have not yielded an association.
In recent years, the association between tobacco and colorectal cancer has been
re-evaluated, including in studies that initially did not support an association but that
had additional follow-up (Giovannucci 2001). In this chapter, the results for an association
between tobacco and colorectal adenoma and cancer are summarized. Evidence
addressing the likelihood of a causal association, and the implications of the findings,
are then addressed.