After the accident at Fukushima Daiichi Nuclear Power Plant, Fukushima Prefecture has started thyroid cancer screening for all citizens who were 18 years of age or younger at the time of the nuclear accident.
Thyroid cancer is found in many people who died for another reason. In other words, thyroid cancer occurs in many people, but most of them remain asymptomatic throughout the lifetime.
Overdiagnosis is the detection of a disease that does not do any harm to the patient throughout the lifetime. Overdiagnosis is likely to lead to treatment that would have been unnecessary without diagnosis. There is also a risk of causing social and psychological harm by being regarded as “sick” people otherwise they would have been able to live as healthy people.
In Korea, after introduction of thyroid cancer screening by ultrasound, the prevalence of thyroid cancer increased up to 15 times, but the mortality rate did not change (Hyeong Sik Ahn et al, Korea’s Thyroid-Cancer “Epidemic” — Screening and Overdiagnosis, NEJM, 2014), and overdiagnosis of thyroid cancer is attracting world-wide attention. Currently, the international consensus about thyroid screening is “not recommended”.
Radioactive iodine from nuclear plants after an accident is a risk factor for thyroid cancer. After the Chernobyl accident, many thyroid cancers were found in children in the nearby area. For this reason, many people were worried about thyroid cancer in children in Fukushima after the Fukushima Daiichi Nuclear Power Plant accident.
Radioactive iodine from the Fukushima Daiichi Nuclear Plant is about 1/10 of the Chernobyl. Further, learning lessons from the Chernobyl, the residents were protected from radiation exposure successfully. For these reasons, the experts thought that the risk of thyroid cancer in children in Fukushima would not increase as in the Chernobyl. However, Fukushima Prefecture has started thyroid cancer screening in order to reduce the residents’ anxiety by setting up a system that allows them to consult immediately if there are any changes in the child’s thyroid.
In 2017, IARC (International Cancer Institute) established the international expert group TM-NUC, which studies the ideal way of thyroid monitoring after a nuclear accident.
In 2018, they came to the conclusion that thyroid cancer screening in the nearby area after the nuclear accident is recommended.
This recommendation is not targeted programs which are already started like the Fukushima thyroid cancer screening. However, if a nuclear accident similar to the Fukushima Daiichi Nuclear Power Plant accident occurs somewhere in the future, thyroid cancer screening will not be recommended.
Louise Davies, MD, a member of TM-NUC and a leading researcher in thyroid cancer overdiagnosis in the U.S.A., says, “There is nothing to stop them (in Fukushima) from using the recommendations,”
How can we make use of international knowledge for the future of thyroid examination in Fukushima? I talked to Dr. Davies.
– I hear that overdiagnosis of thyroid cancer is considered as a problem overseas.
What do you think about thyroid cancer screening program in general?
Yes, overdiagnosis of thyroid cancer has been recognized in several countries, including Canada, the USA, and France, for example.
Thyroid cancer screening programs are not recommended, and I agree with this assessment. Careful study of the data by the U.S. Preventive Services Task Force, most recently in 2017, has concluded that the harms of screening for thyroid cancer outweigh the benefits. The Korean Committee for National Cancer Screening Guidelines reached the same conclusion.
To understand this, it is important to know a few things. First, screening is not just one thing – it is a program: you invite all people in a population who have no symptoms of the disease to get tested for it. The purpose of a screening program is to identify the disease early with a goal of preventing deaths or complications from the disease. For screening to make sense for a population, the disease in general should have a relatively high mortality rate – the burden of finding some disease that might not need to have been treated in these people who had no symptoms must be outweighed by the likelihood that doing so will save their life. Alternatively, if the disease is one in which the mortality is not high (such as in the case of thyroid cancer), finding it early must prevent problems that would arise from the disease if it was found late.
Screening for thyroid cancer is not recommended because the mortality is low, and many people have small cancers that are not growing or are growing very slowly: many people die with a thyroid cancer, never knowing they had it. The USPSTF and the Korean Committee for National Cancer Screening Guidelines concluded that most cancers found with screening would be of this slow or non-growing type. People would get treatment for a cancer that most likely did not need treatment, and population mortality rates would not likely improve substantially – there would not be a population benefit.
-When a patient is overdiagnosed with thyroid cancer, he/she might be suffered mental depression since he/she has to accept the idea that he/she made a wrong choice.
Probably, such a mental effect is more serious in children and their parents than in adults.
What do you think about these mental problems related to overdiagnosis?
This is not easy to answer. Patients whose cancers have already been removed can never know if their cancer was overdiagnosed, because we have no test for this. If their cancer was papillary thyroid cancer, it was causing no symptoms when it was found, and it was small, it is possible that if it was monitored over time without removing it, it might not have become apparent. It is also possible that it might have grown and become a problem later. There is no way to tell in advance which category a person’s cancer will be in.
To avoid regret later, this is why the IARC report recommended that people at risk of developing thyroid cancer after a nuclear accident be offered monitoring, with education about the benefits and harms of such a program. This way people can decide if they want such monitoring, understanding that there is a risk of overdiagnosis, and there is also the potential for benefit for some people if their cancer is found earlier, with less treatment needed.
-It is difficult to make the general public understand the disadvantage of “overdiagnosis”. What factors do you think is preventing people from understanding “overdiagnosis”?
It is hard to understand overdiagnosis for at least two reasons.
One reason is that we tend to think that ‘more is better’ when it comes to healthcare. We have been taught that finding healthcare problems early always means that it is more likely that we can be cured. While this may have been true in the past, our medical care now is so advanced that we can see and find things in the body that in prior years never would have been found, and so may not always need the same kind of intervention that we give problems which come to our attention by causing symptoms.
Overdiagnosis in cancer is even more challenging, because we tend to think of cancer as a disease that will always lead to someone’s death if left without treatment.
We now understand that cancer is not one thing – it has a range of behaviors. It can grow fast and spread, causing a lot of problems, or it can grow slowly (or not at all). Prostate cancer is the best recognized example of a cancer that in some people grows slowly or not at all. Thyroid cancer is another example, and DCIS breast cancer appears to be another example based on emerging research.
– Fukushima Medical University (FMU) is entrusted with FHMS from Fukushima Prefecture. In FMU, one of the doctors claims not like the US or Korea, they can prevent overdiagnosis.
The reason for that claim is that diagnosis and surgery are carried out in more sophisticated ways, for example, they can exclude latent cancer which does not develop for a lifetime by estimating the tumors’ size or existence of metastasis.
Do you think this claim is valid? In other words, do you think that over-diagnosis is now avoided in Fukushima?
As I understand the Fukushima Health Management Survey from the materials I have read and the explanation of the involved scientists, it has been well designed to minimize overdiagnosis and limit over treatment of identified thyroid nodules and cancers. The survey does many things well: for example they are careful not to biopsy nodules that do not need to be biopsied based on size and appearance, and they remove only half the thyroid in the children who undergo surgery. These aspects of the Fukushima program will help minimize the harm that can come from the screening program. Generally speaking however, screening programs always carry a risk of overdiagnosis, because some people will be identified as having the disease, but their disease was mild or was not likely to go on to cause a problem. This is a well understood problem in screening programs, as I described above. The Fukushima Health Management Survey is not an exception. The survey is likely finding some cancers that if monitored over time with active surveillance rather than removed right away might not go on to cause symptoms or spread to nearby lymph nodes. I am not aware of a program of active surveillance in the FHMS at this time. Having such a program would potentially further decrease the rate of overdiagnosis.
-In the surrounding area after a nuclear disaster, can thyroid cancer screening be recommended as an anxiety relief tool?
This is a hard question to answer. After a disaster such as happened in Chernobyl or at the Fukushima nuclear power plant, it is understandable that people want reassurance. However, screening programs bring a different kind of anxiety, because some people will have equivocal results and need further testing or intervention. Furthermore, as I mentioned above, all screening programs have both harms and benefits.
-What do you think can be an alternative?
The IARC task force on which I served discussed this problem at length. We had members who were part of the Chernobyl and Fukushima thyroid screening programs. These members described how strong the requests for a screening program were, because people were very worried about thyroid cancer.
Both groups felt it was very hard to explain to the population the benefits and harms of a screening program, particularly after such a traumatic event. In our report, we recommended that there be a program of ongoing public education about topics such as radiation, what to do after a nuclear accident, who is at risk of developing thyroid cancer after an accident, what is known about the natural history of thyroid cancer and its mortality, and pros and cons of screening programs broadly – not just thyroid cancer but for all diseases. In this way, the local population would be better prepared after such an accident to understand and participate in the accident response and to make choices about how to manage the risk of thyroid cancer.
-There are only few reports on thyroid cancer in children, including those on autopsy.
There is an opinion that “the IARC recommendations are not applicable for the examination of children in Fukushima because they are based on the data from adult.” What do you think about this opinion?
The IARC recommendations were made using data on the outcomes of children from the Chernobyl accident as well as the emerging data on screened children from Fukushima. To say that the report is not applicable to the Fukushima population because it was based on data only from adults is not correct.
-If another nuclear accident like the Fukushima Daiichi Nuclear Power Plant accident will happen in the future, should we recognize that it is recommended that “do not conduct screening tests”, referring to the recommendations of the IARC?
Yes, we hope that communities will recognize our recommendation not to perform population screening, but instead consider offering a program of monitoring to high risk individuals.
We hope that this report will be read and used by communities that have nuclear power plants nearby, so they will be able to be ready to conduct such a program, as it will require long term pre-accident planning. For instance, programs need to be in place for population education prior to accidents, so the population knows what to do should an accident occur. We also recommend that the community have plans to support early, detailed assessments of radiation exposure, so that monitoring (regular thyroid examinations) could be offered to those at greatest risk, as determined by testing and by the goals set by the community.
To summarize: we recommended against population thyroid screening, which we defined as actively recruiting all residents of a defined area, irrespective of any individual thyroid dose assessment, to participate in thyroid examinations followed by clinical management according to an established protocol.
We recommended against population thyroid screening, because the harms outweigh the benefits at the population level. However, we did recommend that consideration be given to offering a long-term thyroid monitoring program for higher-risk individuals after a nuclear accident. This can only be done effectively if the tools are in place to assess radiation exposure. Details of such a program, which include education and methods to measure individual thyroid doses after an accident, are outlined in the report.
-According to the IARC recommendations, “the Expert Group would like to stress that this report is not an evaluation of the thyroid health monitoring activities that were implemented after the past nuclear accidents, and does not include any recommendations related to thyroid health monitoring activities currently in progress, in particular the Fukushima Health Management Survey “. Why was it written like this?
We wrote the report that way because our goal was to make recommendations on the future (not evaluate the past). We learned much from the recent Japanese experience after the Daiichi accident, and this informed the recommendations in the report.
If I were to make a recommendation specifically for Fukushima, I think there would be other things we need to consider such as potential impact of stopping an existing program, whether the residents are still worried about thyroid cancer risk due to the accident, and whether the residents want to keep the program or not, for instance.
-Because of the above words, there is an opinion that “the IARC recommendations should not be applied to thyroid screening in Fukushima Prefecture”. What do you think about the pros and cons of such an idea?
The community members of Fukushima and the scientists overseeing the program should read and absorb the report and then work together to decide whether and how they might want to use the recommendations. There is nothing to stop them from using the recommendations, but a decision should be in conjunction with the community so that the benefits and harms are understood by all and trust is fostered in the process.
-What is your present idea about how we should use the IARC’s recommendations in the Fukushima thyroid examination. In other words, what do you think about the ideal way to modify thyroid screening now undergoing in Fukushima?
The scientists conducting the program should evaluate the benefits and harms of the program based on the data accumulated so far and work with the community as a team to decide how to proceed. Regardless of whether the group decides to change the program or keep it the same, the population invited to participate in the program should receive updated information about the potential benefits as well as harms of participating based on the data gathered so far, so they can make an informed decision. The IARC report may help with creating this information if it is not already being provided, because it outlines both the harms and benefits of population screening programs such as the FHMS.
-What are the benefits for residents in Fukushima and related professionals and administrators by understanding the IARC recommendations?
The IARC recommendations should help the residents of Fukushima and related professionals by creating an opportunity to reflect on the FHMS program and its findings so far, and have a discussion about how they want to manage the program in the future, considering the IARC report recommendations. A tremendous amount has been learned from the program so far, and it should be used to inform the next steps to determine what is right for this community.