Skin cancer: What benefit does positron emission tomography have for treating malignant melanoma?

It is not clear whether positron emission tomography (PET) or PET / computed tomography (PET/CT) improves the treatment of people who have malignant melanoma. It is also not known how exact these procedures are in determining the size, location and spread of a melanoma.

Malignant melanoma, or simply melanoma, is a cancerous tumor that is formed from the skin’s pigment cells (melanocytes). It is also sometimes called black skin cancer. Melanoma is relatively rare, but more aggressive than other types of skin cancer: about 5 out of every 100 skin cancers are melanomas, but they cause the majority of all deaths resulting from skin cancer.

Different things influence the risk of developing melanoma over the course of a lifetime:

• Ultraviolet radiation (UV-radiation) in the form of sunlight or artificial radiation in solariums is a major risk factor.
• Sunburns can also favor the development of melanoma.

Other factors, which we cannot influence by changing our behavior, are

• skin type,
• whether we have many or unusual moles, and
• whether others in the family have skin cancer.

You can find more information about preventing and detecting skin cancer in our feature.

Detecting malignant melanoma

To find out whether someone has skin cancer, the doctor will ask about everything that could influence a person’s risk of getting it. Afterwards, he or she will take a good look at the skin everywhere on the body by following a strict procedure, including the scalp and the mucous membranes of the genitals. If a suspicious change in the skin is found, it will be more closely examined, for example by taking a sample of the tissue and examining it in a laboratory. Or perhaps the suspicious region will be completely removed all at once.

It is assumed that melanomas can be treated more successfully and that fewer people will die of them if they are detected early. If the melanoma is only limited to the uppermost layer of skin, the prospects of full recovery are the greatest. But if, on the other hand, the tumor is growing down deeper below the surface of the skin, it can spread through the blood and lymph vessels into the entire body and form metastases. How dangerous a melanoma will become depends very much on whether and how many metastases it forms, where these are located and how fast they are growing.

Treatment and other examinations, including positron emission tomography (PET)

Many melanomas can be removed by making a small cut in the skin. Yet there are others that are at a more advanced stage when they are detected. Then other treatments, for example chemotherapy, will be needed in addition to removing the suspicious part of the skin.

To see how far advanced the cancer is, imaging techniques are also used. These include ultrasound and x-ray examinations, magnetic resonance tomography (MRT) and computed tomography (CT) scans. Another procedure that uses imaging is positron emission tomography (PET), but it has not yet been routinely used for melanoma.

One possible advantage that PET has over other techniques is that it can detect living cancer tissue because it is measuring the metabolism of the tissue. This way it would be better able to detect tumor tissue that grows especially fast and that can be found in metastases, for example. You can read about how a PET examination works in more detail here.

It is also now possible to combine CT and PET in one machine, called PET/CT. This approach links computed tomography information on the position and spread of the tumor tissue with information about the metabolism gained from the PET scan.

How the benefit of PET and PET/CT is studied

Even though PET does supply more information, this does not automatically mean that patients will have a benefit. The crucial question for people who have malignant melanoma is what effect the results of the examination will have on the overall success of their treatment. Another examination is only medically advisable if it also leads to improved treatment or it helps to avoid unnecessary treatment.

The independent scientific German Institute for Quality and Efficiency in Health Care (IQWiG) – who publish this website – together with researchers from Germany, the UK and the Netherlands, has analyzed trials looking into what benefit PET and PET/CT have in malignant melanoma.

The best way to answer this question is by using a certain type of study: the randomized controlled trial (RCT). In RCTs participants are randomly assigned to one of two or more groups. For example, one group would have a CT scan, and the other would have a PET scan or combination of both. People in each of the groups would then receive treatment according to the results of the examination.

At the end of the trial the results of treatment for both groups are compared. This way we can find out whether one of the two examinations is better suited to finding a successful treatment. You can read more about this here.

The benefit of PET and PET/CT for people who have malignant melanoma is not clear

The IQWiG researchers did not find a single randomized controlled trial that studied how the use of PET or PET/CT affects treatment outcome.

This means that the question of whether people who have malignant melanoma benefit when PET or PET/CT methods are used to detect the spread of tumors or recurrences remains unanswered. Possible benefits would include living longer, experiencing fewer complications from the disease or from the treatment, or having a higher quality of life.

The researchers did find several studies that examined another question: that of whether PET produces more reliable results than computed tomography (CT) for determining the size, location and spread of a melanoma. The researchers found a total of 17 diagnostic studies.

These types of studies try to assess the accuracy of a particular test by comparing different tests with one another. It is important to note that even if one method proves more accurate and more reliable than another, it does not follow that it will automatically lead to better treatment outcomes.

However, the diagnostic studies comparing PET and CT in malignant melanoma were either so varied or so small that they made it impossible to draw reliable conclusions on the accuracy of PET.

It also remains unclear how well PET can detect a recurrence of melanoma – on this issue there was only a single study involving only a few participants.

Overall, it is simply not possible to make statements about the advantages and disadvantages of PET scans for malignant melanoma with any certainty as of yet.

Author: Institute for Quality and Efficiency in Health Care (IQWiG)


Note

This health information is a summary of a scientific report published by IQWiG. It is not an assessment of the right to have health care services paid for by statutory health insurance funds in Germany. By law, decisions about paying the costs for diagnostic and therapeutic procedures can only be made by the German Federal Joint Committee (G-BA). The Federal Joint Committee takes IQWiG reports into consideration in its decision-making process. You can find information about the decisions of the German Federal Joint Committee on its English-language website, www.english.g-ba.de.

© IQWiG (Institute for Quality and Efficiency in Health Care)