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Erika Lindwall: Descriptive Epidemiology of Melanoma
Erika Lindwall
Descriptive Epidemiology of Melanoma
MPH510 Applied Epidemiology
Dr. Carol Hoban, Ph.D.
November 21st, 2014
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I.
Introduction
Every hour, someone in the United States dies from melanoma (Erdei & Torres, 2010). In
fact, cutaneous malignant melanoma (CMM), caused by over-exposure to UV radiation, is the
most dangerous form of skin cancer there is. With an annual increase in incidence rate of 3-7%
among Caucasians worldwide, it has the highest growing incidence rate of any kind of cancer in
the world. About 50,000 new cases are diagnosed each year and about 9,000 deaths occur from
melanoma in the United States. But why is this? Part of the explanation is trending sun-seeking
behaviors without taking necessary precaution. This behavior coupled with the fact that this
cancer is often left undetected makes it a major concern to the epidemiological realm of public
health.
Melanoma forms in the melanocytes of the basal layer of the epidermis. They form when
a mutation in the DNA occurs that causes melanocytes to replicate out of control. This mutation
is caused by exposure to UV radiation. Exposure to UV radiation occurs naturally through
sunlight and artificially through tanning booths. Overexposure to UV light causes sunburns,
which can damage DNA, resulting in mutations that lead to malignant tumors. The tumors that
result from the mutation sometimes grow undetected by the host as they often appear as moles
and brown spots that are small and often appear in regions of the body where they are not seen,
like the back and soles of the feet (Skin Cancer Foundation, 2014). They can also grow in other
pigmented tissues like the intestines and eyes.
Melanoma is diagnosed by taking a biopsy of a suspicious nevus (mole). A suspicious
nevus is characterized by the following standard: asymmetrical and irregular borders of the mole,
color changing or darkening of existing moles, diameter greater than a pencil eraser. Cancerous
moles tend to look different from the other moles in the same region of the body of a particular
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person. They are either lighter in color, darker in color, or appear in a place that has no other
moles around it. This is called the “ugly duckling” principle (Grob & Bonerandi, 1998).
Though it can be very deadly, melanoma has a promising survival rate for those cases
caught in the early stages. In fact, over the course of almost 30 years, the 5-year survival rate has
increased by 11% (Howlader et al., 2013). In 2011, 98.1% of those diagnosed with melanoma
survive after 5 years However, 84% of those diagnosed had melanoma caught in the early stage
of the cancer, before metastasis. What makes this cancer deadly is if it is diagnosed at advanced
stages, in which case, the survival period is less than a year. Only 16.1% of cases diagnosed in
late stages of melanoma survive after 5 years. Death rates for this cancer are highest among those
aged 50+ with a median age at death being 69. This data can be seen in the table below titled
“Percent of Death by Age Group” from Howlader et al. (2013).
II. Host, Environmental, and Temporal Characteristics
Melanoma occurs in all ages 20 and up and in all races. However, it is most common in
men over women, and in fair skinned individuals over dark skinned (Howlader et al., 2013). Fair
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skinned individuals exposed to natural or artificial UV light over long periods of time are where
the cancer appears most prevalently. Others at risk include those with “nevus-prone” bodies,
meaning those with many freckles and moles. A summary of mortality by race and sex can be
seen in the table below “Number of New Cases per 100,000 Persons by Race/Ethnicity& Sex”
from Howlander et al. (2013).
The parts of the body that are most likely to present with melanoma are the trunk and
limbs (Erdei & Torres, 2010). Though there are many influencing factors that contribute to
where melanoma appears including clothing, hairstyle, occupation, and sun-seeking behavior
(Bulliard, Cox, & Elwood, 1997). These factors influence the higher rates of melanoma in the
lower limbs and feet in women, and lesions of the head, neck and trunk areas of the bodies in
men.
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A person’s environment also affects their risk of melanoma. Those with occupations
where they are continually exposed to UV radiation have increased risk of melanoma of the head
and neck (Erdei & Torres, 2010). Those who are intermittently exposed to UV radiation through
recreation and indoor tanning resulting in sunburns have a higher risk of melanoma of the trunk
and limbs. Chang et al (2009) found that recreational sun exposure and sunburn were strong
predictors of melanoma around the globe, occupational sun exposure and total sun exposure were
predictors of melanoma mostly in northern areas.
So, Geography also seems to play a role in incidence of melanoma. In Africa, melanoma
is rare and occurs mostly women on the feet, lower limbs, nail beds, soles of feet, and palms of
hands (Seleye-Fubara & Etebu, 2005). Australia, on the other hand, has the highest incidences of
melanoma in the world. It is seen in both men and women—on the trunk and upper limbs in men
and lower limbs in women (Buettner & MacLennan, 2008). In Europe, the Scandinavian
population was particularly at risk because of their fairer complexion. Here, melanoma appeared
in men and women—on the trunk in men and on the lower limbs in women (Cicarma et al,
2010).
Interestingly, in the Middle East, men are 1.5 times more likely to get melanoma than
women. This is most likely due to clothing differences, as women are required to wear covering
from head to toe. (Noorbala & Kafaie, 2007). This is not so among Arabic men and women
living in the United States. Arabic men and women living in the U.S. have a much higher
incidence of melanoma than their counterparts living in the Middle East, but the incidence is still
much lower than in the Caucasian population. Therefore, there are many different influencing
factors that contribute to a person’s risk for melanoma.
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There are not really any temporal or seasonal variations when it comes to diagnosis of
melanoma. However, there are seasonal variations that change a person’s risk of exposure to UV
light that causes melanoma. Summer months where it is customary to where less clothing and
spend time in outdoor recreation put a person at greater risk overexposure to UV radiation (Erdei
& Torres, 2010).
III. Summary and Conclusions
There are several justifications and explanations for the distributions for melanoma by
race and gender. The main explanation for the distribution of melanoma mostly being in fairskinned people, is that fair-skinned individuals are more prone to sunburn with overexposure to
UV radiations. This is why melanoma is more common in Caucasians more than any other race.
A possible explanation for the gender variation is that men are more likely to be involved in
outdoor occupations, so melanoma is seen to form on the necks and backs of men, whereas
women are more likely to develop melanoma on their legs and feet, as trends in clothing have
exposed legs and feet (Erdei & Torres, 2010).
Though much is known about the oncogenesis, risks, and treatment of melanoma, there
are still gaps in our knowledge. One gap has to do with treatment. In the last few years, two new
drugs have been developed: mutant BRAF inhibitor vemurafenib and the immunostimulant
ipilimumab (Slipicevic & Herlyn, 2012). These drugs are helpful in treatment, especially for
those with late-stage melanoma, but neither drug is sufficient to cure a person of the cancer
completely. There is, therefore, need for improvement in this area through future research.
There are also gaps in our knowledge as to why melanoma forms where it does. It is
different from other skin cancers in its etiology. It is possible that patterns of UV light exposure
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is significant; skin that is exposed occasionally during recreation behaves different than skin
exposed continuously through daily life (Rees, 2008). Furthermore, little is known about how
much of a role climate change plays in the marked increase in melanoma incidence rates. Further
research is needed to determine the answers to these questions as to what influences melanoma
to form.
Malignant melanoma is a problem that is could be given more concern by the public in
general. The incidence rates continue to rise each year and there have not been enough drastic
public health efforts to counteract the growth in this cancer. Efforts need to be made in spreading
awareness, educating at-risk populations about the threat, and funding research on new
treatments. With these kinds of efforts, we will hopefully see decreased cases of melanoma, and
earlier diagnosis for the cases that do occur.
References:
Buettner PG, MacLennan R. (2008). “Geographical variation of incidence of cutaneous
melanoma in Queensland.” Australian Journal of Rural Health. 16:269–277.
Bulliard JL, Cox B, Elwood JM. (1997).”Comparison of the site distribution of melanoma in
New Zealand and Canada.” International Journal of Cancer. 72:231–235.
Chang, Y., Barrett, J., Bishop, D., et al. (2009). “Sun exposure and melanoma risk at different
latitudes: a pooled analysis of 5700 cases and 7216 controls.” International Journal of
Epidemiology. 38:814–830.
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Cicarma E, Juzeniene A, Porojnicu A, Bruland O, Moan J. (2010). “Latitude gradient for
melanoma incidence by anatomic site and gender in Norway 1966–2007.” Journal of
Photochemistry and Photobiology. 101(2):174–178.
Erdei, E., & Torres, S. M. (2010). A new understanding in the epidemiology of melanoma.
Expert Review of Anticancer Therapy, 10(11), 1811–1823. doi:10.1586/era.10.170
Grob, J., & Bonerandi, J. (1998). “The 'ugly duckling' sign: identification of the common
characteristics of nevi in an individual as a basis for melanoma screening.” Arch
Dermatol 134(1):103-104.
Howlader N, Noone AM, Krapcho M, Garshell J, Neyman N, Altekruse SF, Kosary CL, Yu M,
Ruhl J, Tatalovich Z, Cho H, Mariotto A, Lewis DR, Chen HS, Feuer EJ, Cronin KA.
(2013). “SEER Stat Fact Sheet: Melanoma of the Skin.” SEER Cancer Statistics Review,
National Cancer Institute. Retrieved from
http://seer.cancer.gov/statfacts/html/melan.html
Noorbala MT, Kafaie P. (2007). “Analysis of 15 years of skin cancer in central Iran (Yazd)”
Dermatology Online Journal. 13(4):1
Rees JL (2008) Melanoma: What Are the Gaps in Our Knowledge? PLoS Med 5(6): e122.
doi:10.1371/journal.pmed.0050122
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Seleye-Fubara D, Etebu EN. (2005). “Histological review of melanocarcinoma in Port Harcourt.
Niger” Journal of Clinical Practice. 8(2):110–113.
Skin Cancer Foundation. (2014). “Melanoma”. Skin Cancer Information. Retrieved from
http://www.skincancer.org/skin-cancer-information/melanoma.
Slipicevic, A., & Herlyn, M. (2012) “Narrowing the knowledge gaps for melanoma.” Upsala
Journal of Medical Sciences. 117(2):237-43. doi: 10.3109/03009734.2012.658977.