Skin Cancer and Sunlight: Case Control, Cohort, and Clinical Trial Design

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Table of Contents

Skin Cancer Background Information
Literature Review
Case-Control Study
Cohort Study
Clinical Trial Design
Reference List

In epidemiology, researchers can use a number of methods to determine the association between an exposure and a known outcome. These methods include case-controls, cohort, and clinical trials. Over the last century, the incidence of skin cancer has been increasing. Researchers have attributed this increase to sun exposure especially in the age of global warming. This report uses a case-control, a cohort, and a clinical trial design to determine if there is any association between sunlight, which acts as the exposure, and skin cancer that will serve as the outcome.

Skin Cancer Background Information

Skin cancer is a common malignancy affecting the largest organ in the body. Millions of people are affected worldwide. The prevalence of skin cancer in the world as of 2008 was 756,000, with the UK having a prevalence of 67,000 (Situm, Buljan, Bulat, Lugovic, Simic, & Bolanca, 2008). Skin cancer appears in several classes. The type that is most monitored in terms of prevalence is malignant melanoma. The mortality rate for skin cancer is high especially in the United States. In fact, the prevalence of this type of skin cancer in the United States was estimated at 921,780 people in 2013, with an estimated death in the same year being 9,480 people, representing 1.6% of all cancer deaths.

Sunlight Background Information

Sunlight has been associated with the development of skin malignancies, especially with the start of global warming. The main component in sunlight that is said to be responsible for the development of skin cancer is the Ultraviolet emission. Sunlight is a natural occurrence, with all parts of the world having the same occurrence, although in different proportions. The sun, which is a star at the center of the solar system, provides sunlight. Therefore, the prevalence is global and all individuals will be exposed at one time in their life.

Literature Review

Several studies have sought to establish the relationship between sunlight exposure and the development of skin cancer. Some researchers have stated that the ultraviolet rays found in sunlight are responsible for over 90% of the skin cancers, and that a reduction in exposure to sunlight can reduce the risk of developing this malignancy (Roberts, & Black, 2009). This means that sunlight is an invariable cause of skin cancer. People have a higher risk with higher exposure. Some researchers such as Simic, Prohic, Situm, and Zejiko (2010) have proceeded to suggest that the most lifetime exposure to sunlight and ultraviolet rays occurs in adolescence and childhood stages of development. These stages should be targeted in the prevention process of cancer.

As stated earlier, skin cancer constitutes a number of different types of malignancies, which are categorized into malignant melanoma (MM) and non-melanoma skin cancer (NMSC). The sunlight exposure required before these two types of malignancies is different, with researchers stating that longer exposure is needed for the non-melanoma type of skin cancer (Cancer Research UK, 2012a). On the other hand, malignant melanoma easily develops even after a single exposure to sunlight and development of sunburn (Cancer Research UK, 2012b).

There are other risk factors for the development of skin cancer, among them being exposure to radiation, previous non-healing scars, carcinogens such as arsenic, and a reduction in the body’s immunity. However, sunlight exposure remains the single largest and an important risk factor for the development of this malignancy. Some of the other researchers who found sunlight exposure a risk factor for skin cancer are Cho, Rosner, Faskanich, and Colditz. In their research, they looked at one variant of skin cancer, namely the basal cell carcinoma (2005). Some of the other risks that acted in concert with the exposure included an increase in age, family history, and light hair color (Cho et al., 2005).

In their study of the risk factors for cutaneous melanoma, which is another type of skin cancer, MacKie, Hauschild, and Eggermont (2009) stated that a history of severe sunburn was one of the most significant risk factors. They proceeded to state that the exposure time for each individual was linked to the variant of skin cancer that each of these people developed. Other researchers also suggested that the use of Ultra Violet radiation in treatment was a predisposition to the development of skin cancer, and that UV rays were the component responsible for skin cancer in sunlight (Situm et al., 2008). Bath-Hextall, Leonardi-Bee, Somchand, Webster, Delitt, and Perkins (2008) also identified sunlight as a major risk in the development of skin cancer. They cited the example of ex-service people who developed lesions on their necks because of long periods of exposure to sunlight.

Case-Control Study

The research question is, ‘is sunlight exposure a risk factor for development of skin cancer?’ The case control will involve the selection of two groups of subjects based on the outcome. Skin cancer acts as the outcome for this case. The cases will be selected by virtue of being patients with the diagnosis of any kind of skin cancer. Prevalence is the measure of the total number of cases of a certain disease in a population at a given point in time. The cases selected will represent prevalence and not incidence. The cases will also be selected from a population of people suffering from the disease. Such people will not be representing all cases. These cases will be a representative sample where the results can be generalized to the population at risk.

The controls will be selected based on the absence of a diagnosis of skin cancer. An example that may be used to select controls for this study design is the selection of individuals from the list of subscribers to a local insurance plan. These individuals should not have a diagnosis of skin cancer. However, the two groups of subjects will come from the same population since they need to have similar characteristics in terms of the possible experiences. The two groups will not be overmatched. Sampling for the controls and the cases will be done in a manner that is independent of the exposure under study, namely sunlight.

If a control develops the disease while under study, it will be classified as a case, especially if the nested case control study is utilized. The sample of individuals utilized in the study will represent the population exposure level. This sample will be used to determine the actual population that is at risk of developing the outcome. The likelihood of disease misclassification in the determination of the diagnosis is present where patients have inadequate records to support the diagnosis. The case control may have several biases. An example of bias in this case is the selection bias where the participants are not from the same population. Selection bias may also be present if healthy individuals decline to participate in the study as control subjects. Observer bias may also be a possibility in the study. This bias will be evaluated through the development of special tools to collect the data such as questionnaires.

After the collection of the data from the case control, the next step will be to determine whether a relationship exists between skin cancer and sunlight exposure. The first method will involve an analysis of the sample. In a case control, sample analysis depends on the design of the study. Two designs of the case control may be possible, namely individual-matched studies and the unmatched studies (Situm et al., 2008). For the purpose of this case study, the unmatched type is used. Analysis will involve the construction of a frequency table. These tables will show the frequency of skin cancer and the sun exposure in both samples.

At this stage, the frequencies in the tables may be weighed against the available statistics in the population. Otherwise, they can be evaluated to determine whether they correlate. In this case, a 2 × 2 table is constructed by consideration of the exposures that the cases and the controls previously had to sunlight. The measures of incidence including the rate, the odds and the risk will be calculated. The use of case control will be adequate to show the relationship between sunlight and skin cancer. The interpretation of the results will involve the estimation of the odds. If the calculated odds are high, the relationship between the exposure (sunlight) and skin cancer can be deduced. Sunlight can be regarded as a risk factor for the development of skin cancer.

The weaknesses of the study include reliance on the memory of individuals to evaluate their disease status in the absence of adequate records. Another weakness in the study is the relative difficulty in finding the individuals to participate as the control group. The cases are also diagnosed to have the condition, with the control group not having the condition. This finding means that it cannot be used to assess the diagnostic ability of the tests used. The strengths of the cohort study include the fact that it requires less time since the cases are known, and that the outcomes are identifiable. It also has the strength of studying rare conditions to establish their relationship with certain exposures.

Cohort Study

In cohort studies, the association between an outcome and an exposure are determined through the study of the exposed individuals (Situm et al., 2008). The research question is, ‘is sunlight a risk factor for the development of skin cancer?’ Cases will be selected based on exposure to sunlight. Cases exposed to sunlight will constitute the cohort while the controls will be the cases that are not exposed to sunlight. The incidence of the condition will then be calculated with time during the progress of the study. These cases will not represent all cases. Nevertheless, a representative sample of about 200 individuals will be chosen to represent the general population exposed to sunlight.

The cohorts should be selected from occupations that involve being out in the sun for long, especially in the case of service members. The controls will be selected based on limited exposure to sunlight. To aid in this, occupations such as those in the manufacturing industry will be selected. Therefore, sampling as shown will be dependent on the exposure status of individuals, as opposed to the outcome status used in the case controls. If one of the controls develops skin cancer in the course of the study, it will not be considered with the cases, as the qualification is based on the exposure and not the disease. The control will be used to represent the exposure levels of the general population, and hence allow room for the determination of the relationship between exposure to sunlight and development of skin cancer.

In this study design, the researcher will be responsible for the choice of method used to evaluate the presence of skin cancer. Hence, the likelihood of disease misclassification is lower compared to the use of case control studies. Exposure will be assessed based on the number of sunburns that an individual has developed over a given period that will be stipulated in the study. The time will be for the last 5 years before this study. The cohort study will also provide a likelihood of exposure misclassification where the participants who are not exposed to sunlight to the level of developing skin cancer will be included in the study.

The cohort study is likely to have measurement bias where the subjects participating in the study are known to have exposure to sunlight that is adequate to cause skin cancer. This bias is likely if the selection of the population to participate in the study is informed by the presence of the disease in the individuals participating in the study. The bias may be evaluated through the results obtained from the cohort study together with a comparison of the results with the known population standards.

After observing the cohort and the control group for at least 5 years, the presence of skin cancer in these groups will be evaluated. In the analysis of the relationship between skin cancer and sunlight in this study, the first measure to be conducted is the incidence of the disease in the two groups of participants. The incidence of skin cancer in the population that demonstrated more sunlight exposure is weighed against the incidence of the same in the population that was used as the control. The risk of the development of skin cancer in the cohort group can be estimated through the five-year period that the study runs through.

The five-year risk ratio for the two groups exposed to sunlight and those with minimal exposure will then be calculated. To measure the relative and absolute effect, the risk difference and the risk ratio will be calculated (Situm et al., 2008). After the calculation of the ratios in the two populations of participants, a comparison of this prevalence will be made. If the prevalence of skin cancer is higher in the population that was exposed to intense sunlight in the occupation (service members), the interpretation will be that sunlight is a risk factor for the development of skin cancer.

The use of this study to evaluate the relationship between sunlight and skin cancer has several strengths and weaknesses. These elements can be weighed against other study designs such as case controls that have been discussed in the previous section. The major weakness for this form of study is the loss of follow-up that may occur at any stage during the study. The participants in the cohort may opt to withdraw from the study or die in the cause of the study. This provides a challenge with the analysis of the data on skin cancer. Since it requires longer times to follow the participants, the studies can consume a lot of time if the study takes the design of prospective studies such as the one suggested above. Another weakness of the study is the biases that may be introduced in the selection of the participants and the diagnosis of skin cancer in these participants. These biases include selection bias and information bias.

The study design has several strengths over other designs used in this report. One of the strengths is that there is the elimination of biases in the development of skin cancer since the determination of exposure to sunlight is done before the development of the disease. The study can also be used to determine the relationship between the rare exposures in the causation of specific outcomes. In the same study, another strong point is that some of the other exposures that predispose to skin cancer can also be determined.

Clinical Trial Design

The other study design that may be used to evaluate the relationship between sun exposure and skin cancer is a clinical trial. The research question will be, ‘does exposure to sunlight cause skin cancer?’ The type of clinical trial design that will be used is preventive since the study will aim to prevent the development of skin cancer in the population by preventing exposure to sunlight. The clinical trial will also be a community type. The participants will be many as opposed to the use of an individual. The participants to be selected will be those who have had little or no exposure to sunlight together with those who have never been diagnosed with skin cancer. Therefore, the clinical trial will use children who are deemed the least exposed. They will be followed for a number of years to see whether they develop skin cancer. Half of these children will be required to use sunscreen at any time that they are exposed to sunlight. The other half will not be denied sunscreen. However, the study will not make it mandatory for them to use it at all times. Therefore, they will be from areas where people are known not to prefer using sunscreen.

At the onset of the study, both sets of participants will be disease free. A thorough physical examination will be done to rule out any skin cancer or other known risk factors. The physical and medical examination in the other participant groups will also be aimed at ensuring that the two groups are similar in terms of other risk factors related to skin cancer. They will also be from the same geographical areas. This will ensure that the potentially confounding factors are equivalent in these populations.

The exposure levels in these participants are relatively low because they will not have had significant exposure at the beginning of the clinical trial. In this clinical trial, the use of a placebo will not be utilized since it will be unethical to deny the participants an equal chance in the prevention of skin cancer. The study will be a single bling study. The researcher will not know the population of participants who use the sunscreen. However, the participants will be aware of their use of sunscreen. This will make the study a single blinded one.

To ensure that the participants are randomized, they will be selected based on a procedure that provides equal opportunity for selection. The study will use the children in local schools. They will be chosen according to the order of names in the school register. The outcome will be evaluated after a number of years to see the participants that develop skin cancer and those that do not in the population provided with sunscreen and that which does not have access to it. The likelihood of the misclassification of disease is present in this study. However, since the tests to be used will be standard, misclassification will be reduced.

The potential for loss to follow-up is high in this clinical trial because of the long period that the study will run. The results may be affected in the event of any loss to follow-up, thus leading to the introduction of biases in the study. The introduction of biases in this study design is in the selection of the participants. These participants may be selected based on the history of skin cancer in the region where they reside. Another bias that may occur in this clinical trial is information bias. This may be evaluated in the results obtained from the data analysis after the end of the study.

The study will be concluded with an analysis to evaluate whether any relationship exists between sunlight exposure and the development of skin cancer. The two groups of participants will be assessed to see if they have developed pre-malignant skin lesions or any indications of skin cancer. The incidents in these populations for skin cancer will then be calculated, with those that use sunscreen being weighed against the incidence in those that did not use sunscreen. The analysis will involve the calculation of the prevalence in these populations. If there is a higher incidence of skin cancer in individuals who were not required to use sunscreen as compared to the population that had to use sunscreen, the interpretation from this will be that sunlight exposure predisposes to skin cancer.

Just like in other studies, clinical trial has a number of weaknesses and strengths in the evaluation of the relationship between exposure to a particular outcome and skin cancer. These weaknesses were displayed in the study on the relationship between exposure to sunlight and the development of skin cancer. One weakness of the study is the ethical requirements that are tagged with having human subjects to participate in the clinical trial. The participants should be accorded equal opportunities in terms of health benefits. Therefore, it would be difficult to deny one group the treatment that it deserves. The study is also predicted to take a very long time, as the children will have to be followed throughout their lives to see the relationship.

However, the strengths of the study design include the fact that the association between sunlight exposure and the development of skin cancer can be made. In the process of forming an association between sunlight exposure and skin cancer, other variables in the causation of skin cancer can be established in the study. The other strength of using clinical trial design to evaluate the relationship between sunlight and skin cancer is that the protective properties of sunscreen used in the study can be evaluated. A confirmation of the research done on it is hence possible. The data provided can also be used for other studies that will follow the evaluation of the relationship between sunlight and skin cancer.

Reference List

Bath-Hextall, F., Leonardi-Bee, J., Somchand, N., Webster, A., Delitt, J., & Perkins, W. (2008). Interventions for preventing non-melanoma skin cancers in high-risk groups. Cochrane Database of Systematic Reviews, 17(4), CD005414.

Cancer Research UK (2012a). Skin Cancer Risks and Causes. Web.

Cancer Research UK (2012b). Melanoma Risks and Causes. Web.

Cho, E., Rosner, B., Faskanich, D., & Colditz, G. (2005). Risk factors and individual probabilities of melanoma for whites. Journal of Clinical Oncology, 23(2), 2669-2675.

MacKie, R., Hauschild, A., & Eggermont, A. (2009). Epidemiology of invasive cutaneous melanoma. Annals of Oncology, 20(6), vi1-vi7.

Roberts, C., Black, D. (2009). Comparison of interventions to reduce sun exposure. Behavioral Medicine, 35(2), 67-76.

Simic, D., Prohic, A., Situm, M., & Zejiko, P. (2010). Risk factors associated with the occurrence of basal cell carcinoma. Collegium Antropologicum, 34(1), 147-150.

Situm, M., Buljan, M., Bulat, V., Lugovic, M., Simic, D., & Bolanca, Z. (2008). The role of UV radiation in the development of basal cell carcinoma. Collegium Antropologicum, 32(2), 167-170.

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