Head and neck tumors: Is a PET examination more exact than routine examinations, and does it lead to better treatment?

It is not yet clear whether cancer in the head and neck region can be diagnosed more precisely by using positron emission tomography (PET) or PET / computed tomography (PET/CT), and whether recurrences can be more reliably detected than is possible with standard examinations. It has also not been possible to estimate what kind of an influence it has on the success of treatment.

The risk of malignant (cancerous) head and neck tumors is relatively low: it is estimated that in Germany 29 out of every 100,000 men and about 8 out of every 100,000 women will develop these tumors per year. This means that out of the entire population there are still several thousand people who develop this type of cancer every year.

“Head and neck tumors” is a collective term covering different types of cancers, for example cancer of the larynx, the pharynx, or of the mouth.

Sometimes a malignant tumor is discovered in a lymph node in the neck area that has its origins in another part of the body. This means that these cancer cells were carried through the lymph vessels and have settled in the neck. This newly growing tumor is called a metastasis. Sometimes the original tumor cannot be found; in this case, doctors refer to an unknown primary tumor.

Examinations for head and neck tumors

Depending on where the tumor occurs, it can cause different types of symptoms. A tumor in the larynx may be noticeable because it causes hoarseness or breathlessness. Some of the symptoms can be quite general.

If a tumor in the head and neck region is suspected, after a physical examination and a review of the medical history, imaging techniques are used to detect a possible tumor or whether it has spread. For metastases in the throat region, this may also be done to discover the primary tumor. The imaging techniques usually include ultrasound (sonography), computed tomography (CT) and/or magnetic resonance tomography (MRT). A tissue sample is also taken in order to determine whether the tumor is indeed cancerous.

PET has not yet been routinely used in examinations for head and neck tumors.

The special thing about PET: it shows how active the metabolism is in the body’s different tissues. It can detect cells or tissue that use a lot of energy and have a high level of metabolism, including tumorous tissue. Also, a CT or MRT image often does not show a difference between new “active” tumor tissue and the remains of old “inactive” tumor tissue that has already been killed by radiation. This fact could help to evaluate the effect of treatments faster, for example.

You can read more detailed information about what happens during a PET examination here (URL: http://www.informedhealthonline.org/index.743.en.html) .

It is now also possible to combine CT and PET in one device, which is then called PET/CT. This links the anatomical information from computed tomography to the metabolic information from PET. Doctors hope to use this new technique to already find tumors when they are still very small.

How the benefit of PET and PET/CT is tested

This poses the question of whether people who have head or neck tumors might profit from examinations using positron emission tomography or PET/CT. The German Institute for Quality and Efficiency in Health Care (IQWiG) – who publish this website – evaluated studies on this topic together with researchers from the University of Basel.

The main goal of this evaluation was to find out whether people with a head and neck tumor profit from a PET or PET/CT exam, by having their treatment improved using the results of the examination.

Randomized controlled trials provide the most conclusive results

For people with head and neck tumors, the truly important question regarding a new method of examination is whether the results will also have an influence on the treatment and its success. An extra examination only makes sense medically if it can also lead to better treatment.

This question can be answered by using what are called randomized controlled trials. There are different ways of doing these types of trials. One way is to randomly divide volunteers into two or more groups. Then in one group, for example, computed tomography will be done, and in the other positron emission tomography or a combination of both. After the examination, the patients are treated according to the results of their examination. At the conclusion of the trial the results of treatment for both groups are compared. This will show whether one of the two examinations is better for finding a successful treatment. Scientists nowadays regard these types of trials to be the best research method for testing medical techniques for diagnosis and treatment. You can read more about how randomized controlled trials are done here (URL: http://www.informedhealthonline.org/index.61.en.html) .

Benefit of PET or PET/CT for people with head and neck tumors is not clear

According to the evaluation of the available research, the effect of PET or PET/CT on treatment success, and thus the benefit of this type of examination for those affected by these tumors, cannot be determined exactly: the researchers did not find a single randomized controlled trial on PET or PET/CT in head and neck tumors.

Only 1 less conclusive comparative study had the goal of assessing the immediate benefit of this technique for people with head and neck tumors: it tested whether people remained free of recurrences longer after having a PET exam than people who did not have a PET exam. But by involving only 102 participants this study was relatively small and also had methodological weaknesses. Also, there were only 10 recurrences in total: 6 in people after they had PET, and 4 in people who did not have PET. These minor differences could have easily occurred by chance and do not allow any firm conclusions to be drawn.

The researchers also tested whether a PET or PET/CT examination provides more reliable results than a CT exam. To assess the precision of an examination, so-called diagnostic studies are needed, which compare different examinations with one another. It is possible, for example, to test whether a PET examination can determine the size and location of a tumor more accurately than a CT examination, and thus produce more reliable results.

The result: the accuracy of PET and PET/CT compared with other examinations was indeed tested in a number of diagnostic studies. But these types of studies are not suited for examining the benefit of the examination for people who have a disease. Many of these studies also had different methodical errors. In some situations it is still not clear whether the use of PET and PET/CT has an advantage for patients, even if tumors are found that were not detected using other methods. This applies, for example, to patients with cancer in advanced stages, where metastases were found in the head and neck region, but the primary tumor was not able to be located using other methods. These unknown primary tumors may possibly be found using PET and PET/CT. To what degree this has a positive effect on treatment and prognosis for patients, remains an unanswered question.

Overall it is not possible to say with certainty anything about the advantages and disadvantages of PET and PET/CT examinations in head and neck tumors.

Author: German 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 reimbursed by statutory health insurance funds in Germany. By law, decisions about the reimbursement of 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 (URL: http://www.english.g-ba.de/) .