Narrator: Hi everyone, and welcome to today's lecture
on the epidemiology of laryngeal cancer.
In today's lecture, we have several goals.
We're going to describe basic laryngeal
anatomy and function.
We'll describe the global pattern
of laryngeal cancer mortality and incidence.
We are going to review trends of laryngeal cancer
in the US, describe synergisms of alcohol and tobacco,
review studies of HPV and laryngeal cancer,
and describe laryngeal cancer prevention and control.
To begin with and to give a brief overview
of the anatomy of the larynx,
the larynx has three anatomic divisions,
the supraglottis, the glottis, and the subglottis,
which we can see here.
The supraglottis consists of the epiglottis,
the false vocal cords, the ventricles,
and the aryepiglottic folds.
The glottis includes the true vocal cords
and the anterior commissure.
And finally, the subglottis is located
below the vocal chords and extends approximately
five millimeters into the trachea.
So looking at the male incidence of laryngeal cancer,
we see the cancer of the larynx occurs over seven times
more often in men than women.
Globally in 2012, laryngeal cancer was diagnosed
in 108 or 138,102 men
compared to only 18,775 cases in women.
It also caused 73,126 deaths in men
compared to 10,115 deaths in women.
Among men, cancer of the larynx comprised approximately 1.9%
of all cancers and was responsible for 1.6%
of all cancer deaths.
Among women, the malignancy accounted
for only 0.3% of all cancers and cancer deaths.
Turning to look at the mortality, we see that the incidence
of mortality rates of laryngeal cancer are highest
in populations with the highest chronic or highest rates
of chronic tobacco smoking and alcohol abuse.
In particular, male populations characterized
by heavy smoking and drinking, such as in Cuba, Poland,
Hungary, Romania, Turkey, Turkmenistan,
Kazakhstan, Croatia, Russia, Spain, Italy,
Portugal, and Brazil have incidence rates
that are four to seven times higher
than the average global rate of 1.9 per 100,000,
and we see these countries highlighted
in the darker blue color.
In the US in 2020, the age-adjusted incidence
of laryngeal cancer was two per 100,000 overall,
with an incidence of 3.6 per 100,000 in men
and 0.49 cases per 100,000 females.
The mortality was one per 100,000 overall,
1.9 per 100,000 men and 0.28 per 100,000 females.
So as we've discussed before, the Surgeon General's
1964 report, "Smoking and Health",
touched upon lung cancer and laryngeal cancer.
The report found that there was a 1.7-fold increase
in all-cause mortality with a 10-fold increase
in mortality for lung cancer and a 20-fold increase
in mortality for heavy smokers.
The key finding related to laryngeal cancer
was that there was a 5-fold increase in mortality
for people who smoked compared to those who don't smoke.
So looking at the trend of incidence in the US
over from 1980 to 2010, we see that the annual incidence
of laryngeal cancer has declined by about 40%
in the US since 1990.
This trend has occurred concurrent with sharp declines
in the prevalence of cigarette smoking in US men and women
and during 1980 to 2011, the prevalence of smokers
decreased by 40% in men, from 35% to 21%,
and by 43% in women, from 30% to 17%.
While the relative declines are similar by gender,
the data continue to reflect a four to five-fold excess
of incident cases in men compared to women.
Looking at the age distribution of laryngeal cancer,
we see that most cases, or 97% of cases,
are diagnosed after the age of 45 years.
The peak ages of onset are between 55 to 75 years
during which about 58% of cases are diagnosed.
Nevertheless, certain subtypes of laryngeal cancer
are being diagnosed at earlier ages.
For example, those related to HPV infection
manifest on average about four years earlier
than those associated with tobacco and alcohol.
We also see a relationship between laryngeal cancer
and smoking and this has been compared between,
or comparisons have been drawn
between filter and non-filter cigarettes.
So we know that chronic cigarette smoking
markedly increases the risk of developing laryngeal cancers,
and among chronic smokers,
there's a dose response relationship between the number
of cigarettes smoked per day and the risk
of developing laryngeal cancer and the dose response holds
for smokers of both filter and non-filter cigarettes.
We also see that chronic alcohol abuse
markedly increases the risk of developing laryngeal cancer.
Among regular drinkers, there is also a dose response
relationship between grams of alcohol consumed per day
and the risk of developing laryngeal cancer.
Finally, we see that there's a synergistic relationship
between chronic cigarette smoking and alcohol abuse
and risk estimates approximate
a multiplicative model of synergism,
as we can see in this figure
where people who are consuming more than four or more drinks
per day and 30 or more cigarettes per day
have a relative risk that is many times higher
than any other condition on this graph.
We also know that a subset of laryngeal cancers
arise due to chronic infection
by oncogenic strains of HPV, being HPV16 and HPV18.
HPV-related cases tend to be diagnosed
at younger ages than those with tumors
arising from exposure to tobacco and alcohol.
The key primary prevention steps
for laryngeal cancer are to avoid smoking tobacco,
avoid excess alcohol consumption,
avoiding HPV infection, and being vaccinated by HPV,
for HPV16 and HPV18.
We'll discuss more about vaccination campaigns
against the multiple strains of HPV
in our lecture about cervical cancer later in the course.