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Thyroid
Cancer Epidemiology

Nicholas
Foggia

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MSCC-
503 Cancer Epidemiology

Saint
Francis University

December
11, 2017

 

 

 

 

 

 

 

 

 

 

 

Thyroid
Cancer Epidemiology

Abstract        

Thyroid
cancer is a common tumor type that has increased over the years around the
world and in the United States. This tumor is found in the thyroid gland that
is located at the bottom of the throat and is known as an endocrine cancer or
tumor. The reasoning behind being labeled an endocrine tumor is because of the
role the thyroid has in the human body regarding growth and metabolism. The
thyroid is an important gland because of the hormones it releases that help the
body grow as well as regulate certain functions within the body. With such an
important role to the maturation and growth of a person, is it safe to assume
that thyroid cancer is an incredibly dangerous diagnosis with little chance of
survival? On the contrary, thyroid cancer is one of the less dangerous cancers
with a positive prognosis. While all cancer is serious, this cancer has a
silver lining by its survival rate even though it seems to be growing over the
past year. This cancer has a higher incidence rate in women and minorities and
this could be because of certain risk factors that put people at a higher risk
of developing thyroid cancer. With these risk factors in mind there are certain
prevention measures that can be taken in order for a person to be at a
decreased risk of cancer.

 

 

 

 

 

Thyroid
Cancer by the Numbers

            Thyroid cancer, like many other cancers has increased
over the past couple decades and in prevalence but has remained very much
similar in terms of the survival rate. Based off of recent statistics the
prevalence of thyroid cancer is roughly around 725,000 people as of 2014. The
number of new cases in cancer has also increased over the past decades with
roughly around 0.5 per 100,000 people being diagnosed with thyroid cancer per
year. It is estimated that there will be upwards of 56,000 new cases of thyroid
cancer diagnoses in the year 2017. This estimate would make up about 3.4% of
all new cancer diagnoses in the current year. 1

            While these numbers seem daunting thyroid cancer does not
even rank in the top ten types of cancer. Thyroid cancer is the eleventh most
common type of cancer in the United States with breast cancer in females and
lung and bronchus cancer at the top of the list. Both breast and lung and
bronchus cancer have an estimated new cases in 2017 of over 200,000 diagnoses.1,2
This is almost four times the incidence of thyroid cancer (almost 57,000 new
cases in 2017). While this shows that thyroid cancer is not as prominent as
some other cancers it is still an area that obviously needs attention.

            The numbers behind thyroid cancer can be a little
confusing because while the cancer is the eleventh most common cancer in the
United States it actually as a positive survival rate. The five-year survival
rate of this cancer is 98.2% which sets an optimistic outlook on this disease.
However, this survival rate is not set at this positive value because the
survival rate can be affected by stage. The further the stage of the cancer the
lower the five-year survival rate in thyroid cancer. When the cancer is
localized, or has not left the thyroid, the five-year survival rate is close to
absolute at 99.9% and when the cancer has spread locally to the lymph node
within the area then there is a 98.0% five-year survival rate. Unfortunately,
like most cancers, when the cancer cells spread to a distant region in the body
the survival rate decreases. Specific to thyroid cancer, when the cancer cells
metastasize to a distant place in the body there is a 56.4% five-year survival
rate. Luckily the majority of thyroid cancers are found in early stages with
68% of it staying within the thyroid and 27% of it staying in the lymph nodes
around the thyroid. 2

            Like most cancers there are certain people who are at a
higher risk of being diagnosed than others and thyroid cancer is no different. Thyroid
cancer is mainly diagnosed later on in life with a dramatic increase in ages
45-54. This peak range accounts for 23% of all thyroid cancer diagnoses and the
mean age of thyroid cancer diagnoses is 51 years of age. In addition to age
being an increased risk factor for thyroid cancer, gender is also of increased
prevalence.2 In women there are 21.0 new cases per 100,000 people as
compared to 7.1 new cases per 100,000 people in men. This is in all races but
there is also an increased prevalence in people who are white, Hispanic and
Asian/Pacific Islander.2

            While the average age of diagnoses of this cancer is 51
years of age the average age of death of thyroid cancer is 73 years of age.
Even though the highest age group of diagnoses is 45-54 the highest age rate
for death is 75-84 years of age.2 The number of deaths per 100,000
people is actually fairly even among races.

             Hawaii is also at
an increased prevalence and incidence because it is considered a regional
factor. A study done in 2013 looked at the descriptive epidemiology of thyroid
cancer in areas with volcanoes and found that these areas were at an increased
incidence.3 A reason that this could possibly be is because the
environmental factors that are influenced by the volcanos can be considered
carcinogenic.3 These can be considered carcinogenic because they may
be endocrine disruptors which can disrupt the natural function of tissues and
become cancerous mutations.

Relative
Risk in Thyroid Cancer

            While there are several risk factors that are attributed
to thyroid cancer certain factors have a higher risk than others. Using a
literary review several relative risks were assessed to determine the
probability of being diagnosed with thyroid cancer when exposed to these risks.
According to the American Cancer Society some of the more common risk factors
that have already been discussed have been discussed such as age and gender. Several
other exposure factors such as smoking an alcohol consumption are known to have
adverse health effects in areas other than thyroid cancer but studies have also
been done in order to assess how great of a risk these things have on this
specific cancer type.

Relative
Risks

Cigarette
Smoking

Study

Relative
Risk

Current
or Former Smoker

Mack

0.6

Current

Mack

0.9

Former

Rossing

0.5

Current

Rossing

0.7

Former

Kabat

0.57

Current

Kabat

1.16

Former

Table 1. Cigarette
Smoking and Relative Risk

 

 

Alcohol
Consumption

Study

Relative
Risk

Study
Type

Seung-Hee Hang

0.74

Observational

Seung-Hee
Hang

0.77

Case-Control

Seung-Hee Hang

0.70

Cohort
Study

Seung-Hee
Hang

0.82

Cross Sectional

Wang

Inverse
Relationship

Mack

Inverse Relationship

Rossing

0.7

Kabat

0.67-0.97

Table 2. Alcohol
Consumption and Relative Risk

 

Caffeine
Consumption

Study

Relative Risk

Han

0.88/0.59

Mack

0.6

Table 3. Caffeine
Consumption and Relative Risk

 

 

 

Diet
Factors

Study

Relative Risk

Cho

1.43*

Table 4. Dietary Factors and Relative Risk

(* denotes a significant relative risk)

 

 

 

 

Hormonal
and Goiter Factors

Study

Relative
Risk

Menopause

Schonfield

1.22

Surgical

 

1.00

Natural

 

1.29

>55
years at Natural Menopause

 

1.26

45-49
years at Surgical Menopause

 

1.26-1.63

MHT
Use

 

1.47

Benign
Breast Disease

Goiter-Truong

4.2

Goiter

Table 5. Hormonal Factors
and Relative Risk

 

 

 

 

 

 

 

Age:

            Age is a common risk factor among several types of cancer
and thyroid cancer is no different. It is very common that the older a person
gets the more likely it is that they are at risk for thyroid cancer.4,5
A study done in 2015 showed that risk of multinodularity risk of thyroid cancer
increased by 1.6% each year with a relative risk of 1.022.5

Gender:

            As mentioned before, women have a greater risk of
developing thyroid cancer as compared to men. The overall relative risk for
thyroid cancer in both men and women in the United States has been calculated
to be 2.9 but the risk for women is four times greater than it is for men.5
It is not completely clear as to why thyroid cancer is more common in women as
to men but with this knowledge more preventative measures can be taken for this
specified group at risk.

Hormonal Effects and
Goiter Effects:

            Hormonal effects are one of the most common risk factors
for those who develop thyroid cancer. It is shown that some of these risk
factors include; age at natural menopause, age at surgical menopause and status
of menopausal hormone therapy. Table 5 describes the relative risk within these
risk factors.6,7 Another important but not common risk factor is the
effect a goiter can have on a person’s risk of thyroid cancer. Goiters are an
abnormal growth of the thyroid gland that can be visible from a person’s neck
area. This growth of the thyroid can be explained by an imbalance of hormones
in the thyroid that causes it to grow. () While goiters are not overly common
it still can place a person at a higher risk of developing thyroid cancer. A
study was done that examined this risk based on the history of people who had a
goiter. Those who had a goiter had a significant relative risk of a 4.2.17,18
This means that a person with a history of a goiter is more than 4 times
likely to have thyroid cancer than someone who does not share this same
history. These studies show that hormonal effects play a major role in the risk
of thyroid cancer and should not be taken lightly.17

Smoking in Thyroid
Cancer:

            While smoking has adverse health effects in different
areas of human life it is not always the case with specific types of disease.
While greater risk factors in thyroid cancer such as age and gender exist there
have been several studies done to assess the relative risk of smoking and
thyroid cancer.11,12,13 The studies found in Table 1 all represent
an analysis of the different studies that have been done in order to assess
this risk. Many of these studies separated the risk by those who are current
smokers, previous smokers and some even by those who have not smoked before.
Within this review it was shown that smoking does not have a high relative risk
in terms of thyroid cancer. Looking at the table the ranges of relative risk in
current smokers is an RR of 0.5-0.6 and former smokers is 0.7-1.16. This shows
that there is not a strong relative risk among those who smoke and those who
are diagnosed with thyroid cancer.

Alcohol in Thyroid
Cancer:

            Very much like smoking, alcohol has been known to have a
negative effect in certain areas of health related disease and outcomes. The
several studies that have been done about alcohol and the relative risk of
thyroid cancer have shown similar results to that of the smoking and even
suggest that alcohol may serve as a protective factor to the risk of thyroid
cancer.8,12,13 Table 2 shows that these relative risks of the
alcohol are all below 1.0 (0.6-0.82). This suggests that there may even be a
protective factor between alcohol and thyroid cancer.

Coffee/Caffeine in
Thyroid Cancer:

            When examining if coffee drinking or caffeine intake
makes one a greater risk of developing thyroid cancer a similar finding to
alcohol and smoking is found once again. In Table 3 it shows that in these two
studies the relative risk of caffeine intake was 0.59-0.88, meaning that it
does not put a person at greater risk of developing this cancer.9,10  

Diet/Diabetic/ Physical
Activity factors in Thyroid Cancer:

            Diet and lifestyle habits can also have an effect on
whether or not someone is at an increased effect of being diagnosed with
cancer. Some dietary factors included a diet that involves an
iodine-deficiency. A study that was conducted showed that there was an
increased risk of thyroid cancer with an iodine deficiency, RR= 1.43. Studies
have also taken a glance at physical activity levels of individuals and have
been back and forth on the results of whether or not physical activity levels
have a significant reduction or attribution to risk.14 When diabetes
was observed it was found that certain studies showed a statistical relative
risk while others did not.15 (Table 4). Studies have also been done
in order to assess possible risk factors of physical activity and thyroid
cancer. While physical activity has a great effect on many areas of health and
disease prevention there was no significant risk or even reduction of risk that
was found between the two.14,15

Radiation in Thyroid
Cancer Risk:

            Radiation is also listed as a significant risk factor for
thyroid cancer. This risk can be separated between certain age groups at the
time of radiation. Studies have also observed the risk of radiation exposure
and other neck and chest cancers.16 In a specific study in 2005 it
was observed that with thyroid cancer the older a person was when they were
exposed the more likely they were to get thyroid cancer.16 This
study also took a look at thyroid cancer as a second primary cancer diagnoses
as a result of the treatments of other cancers. Those who have received
radiation therapy to combat and treat other types of cancer have a significant
increased risk of developing thyroid cancer in the future.

            This analysis of specific risk factors for thyroid cancer
has shown that this specific disease has different and specified risk factors.
Many diseases have a greater risk factor when it comes to age and even gender and
thyroid cancer is no different, as these risk factors are two of their greater
contributors. Other significant risk factors in this disease include dietary
lifestyle habits, hormones and radiation and can increase the likelihood of a
person being diagnosed. Some risk factors that have been studied but have not
proven to be significant risk factors include; caffeine intake, alcohol
consumption and smoking. These factors may have a significant risk in other
diseases but in thyroid cancer it has not been proven to be a risk factor.
Epidemiologically, alcohol and caffeine intake has actually had a low enough
relative risk to be possibly considered a protective mechanism of thyroid
cancer. With the knowledge of what puts people at a higher risk of thyroid cancer,
preventative measures can be implemented in daily living to avoid a possible
future diagnoses.

Prevention
of Thyroid Cancer:

            Thyroid cancer has several risks associated with it and
because of this there can be certain steps that are taken to reduce a person’s
risk. There will be certain risk factors that can be modified and changed and
there are certain risks that cannot be changed. Even though there are factors
that cannot be changed there is still preventative measures that one can take
in order to decrease the risk of developing thyroid cancer.

            The risk factors that are non-modifiable for thyroid
cancer include age and gender. A person cannot change their age, nor their
gender so it is not something that a person can attempt to adapt to in order to
avoid risk. Other risk factors that cannot be controlled for are also heredity
conditions and family history of thyroid disease. These factors put certain
people at a predisposed increased risk of thyroid cancer and cannot be changed.
Because these risks cannot be changed or decreased then the risk factors that
are modifiable should be taken seriously and lifestyle habits can be changed.

            Some of the risk factors that can be changed in order to
reduce the risk of thyroid cancer include dietary factors, hormonal factors and
radiation. There are several dietary factors that go into thyroid cancer risk
such as obesity and iodine deficiency. Preventative measures that could aid in
this could be weight loss programs that could not only decrease risk of thyroid
cancer but also decrease the risk of other chronic diseases. These programs can
include group exercise classes with dietary seminars that can improve body
composition and overall health. The iodine deficiency risks could be handled by
also holding dietary seminars that show the importance of eating foods that are
sufficient in iodine. These foods can include the healthier areas of the food
groups such as vegetables and fruits. Another option for this could be iodine
supplementation for those who have the knowledge that they are iodine
deficient. These risk factors are some of the more feasible ones that can be
fixed and altered to reduce risk.

            One of the more important risk factors that can reduced
is the radiation exposure factor. Because radiation is a very high risk factor
in thyroid cancer it is important to reduce the exposure of it throughout the
lifetime of a person. According to the United States Nuclear Regulatory
Commission (U.S.NRC) the top two causes of exposure of radiation in the United
States comes from Radon exposure, 37%, and from medical procedure, 36%.19
Because these exposures are so high it is important that individuals and
nations are taking the proper steps in order to reduce these risks. Radon is a
radioactive chemical that is toxic to the human body especially after prolonged
periods of time. It is found greatly in homes because it escapes rocks and soil
and traps itself in closed spaces like houses.20 There are several
agencies such as the International Radon Project and the World Health
Organization that are looking to increase the awareness of radon levels and
exposure so that homeowners can be aware of the risk and be conscious of
preventing these levels to increase.

Conclusion:

            Thyroid cancer prevalence and incidence has been
increasing of the years but there are ways that this cancer can be beat. This
specific cancer has a very good survival rate which brings hope to those who
have been diagnosed with this cancer. Taking preventative measures such as
dietary regulation and avoiding radiation exposure when possible can help
reduce the risk that one has at coming down with this cancer.

 

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