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The Examiner

August 11 2009

On an intuitive level, it makes sense that people who smoke cannabis
might face similar elevated risks for head and throat cancers as do
those who smoke tobacco, and/or drink alcohol. Both alcohol and
tobacco use carry significantly higher risks for such cancers.

Much has been made of a 1999 study which indicated that cannabis
users might face some elevated risk of head and neck cancers. However,
even the researchers from that study cautioned against making too much
of their results and called for further study.

However, two recent studies indicate that, not only do cannabis users
face no increased risk of head and neck cancers, they seem to enjoy a
measure of protection, as witnessed by a reduced risk for head and
neck cancers among moderate cannabis users. Moreover, that protection
seems to extend to those who smoke tobacco and drink alcohol.

In the first study, a team of researchers set out to determine
whether cannabis smoking actually increases the risk of head and neck
cancer. The research team included S. Aldington, M. Harwood, B. Cox,
M. Weatherall, A. Pritchard, G. Robinson, L. Beckert, A. Hansell, and
R. Beasley, along with nearly 20 other collaborators.

The group used hospital databases and the Cancer Registry to identify
cases of head and neck cancer in patients aged 55 years or under, and
to compare those cases to a control group randomly selected from
completed interviewer-administered questionnaires.

They designed a case-control study that used logistic regression
analysis assess relative risk levels for head and neck cancer. The
team followed 75 cases and 319 controls. They found elevated cancer
risks associated with tobacco use, alcohol consumption, and lower
income but none with cannabis use.

Even heavy cannabis users (>8.3 joint years) showed only a
statistically insignificant increase in cancer risk (relative risk =
1.6, 95% confidence interval, 0.5-5.2), after adjusting for
confounding variables.

The results showed that cannabis users faced no greater risk of head
and neck cancer compared to controls. However, due of the limited
power and length of use studied, a small or longer-term effect cannot
be ruled out.

In the second study, researchers conducted a comprehensive
population-based case-control study of marijuana use and head and neck
squamous cell carcinoma. The research team was made up of C. Liang, M.
D. McClean, C. Marsit, B. Christensen, E. Peters, H. H. Nelson, K. T.
Kelsey of the Department of Community Health, Department of Pathology
and Laboratory Medicine, Division of Biology and Medicine at Brown
University.

Scientists recognize the fact that cannabinoids, the active
components of marijuana smoke, have potential antitumor properties.
However, clinical evidence on the exact relationship between marijuana
use and the induction of head and neck squamous cell carcinoma (HNSCC)
has been inconsistent and conflicting.

The Brown University study looked at 434 patients with incident HNSCC
disease from nine medical facilities in the Greater Boston area
between December 1999 and December 2003. They matched a group of 547
control subjects for age (+/-3 years), gender, and town of residence,
randomly selected from Massachusetts town books.

Participants answered a questionnaire on lifetime marijuana use that
detailed decade-specific exposures, and were evaluated using
unconditional logistic regression.

After adjusting for potential confounding factors (including tobacco
smoking and alcohol consumption), the research team found that 10 to
20 years of marijuana use was associated with a significantly REDUCED
risk of HNSCC [odds ratio (OR)(10-<20 years versus never users), 0.38;
95% confidence interval (CI), 0.22-0.67]. Among marijuana users
moderate weekly use was associated with reduced risk (OR(0.5-<1.5
times versus <0.5 time), 0.52; 95% CI, 0.32-0.85).

The magnitude of reduced risk was more pronounced for those who
started use at an older age (OR(15-<20 years versus never users),
0.53; 95% CI, 0.30-0.95; OR(> or =20 years versus never users), 0.39;
95% CI, 0.17-0.90; P(trend) < 0.001). These inverse associations held
independent of human papillomavirus 16 antibody status. However, for
the subjects who have the same level of smoking or alcohol drinking,
we observed attenuated risk of HNSCC among those who use marijuana
compared with those who do not.

The data from this study shows that moderate marijuana use is
associated with reduced risk of HNSCC. Basically, both of these
studies support a growing body of data that indicate cannabis to have
anti-tumor and anti-cancer properties. Clearly, further study is
warranted.