Answers to frequently asked questions about juvenile thyroid cancer
Q1 Is the number of patients with thyroid cancer in Japan increasing due to the effects of radiation?
A1 Experts believe that thyroid cancer is not increasing.A report from the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) says there is a very low possibility that the number of patients with thyroid cancer will increase due to the effects of radiation.
Q2 I heard that thyroid cancer in young people progresses rapidly. Is it dangerous?
A2 Thyroid cancer in young people shows an excellent prognosis.Thyroid cancer in young people is usually found at a stage when symptoms are already present. It presents as a large lump in the neck, and it often accompanies local and distant metastases. The recurrence rate after surgery is higher than that of thyroid cancer found in older people. However, thyroid cancer in young people responds very well to treatment. The 5-year survival rate is almost 100%, and the lifetime survival rate is 95% or more, which is the best result of all cancers.
Q3 Does a small thyroid cancer that happens to be found by ultrasonography at a young age will turn into a more dangerous disease if left untreated for several decades?
A3 Most of the small thyroid cancers in young people are unlikely to turn symptomatic after middle age.Ultrasound examination often finds a small thyroid cancer in adults after their thirties. They are thought to have occurred in teens and 20s. Currently, more than 1,000 cases with such a disease have been observed without surgery for decades. As a result, most of these cancers did not grow larger. Further, no patient has died of thyroid cancer, and none of them has changed to an undifferentiated or anaplastic carcinoma. Data that the mortality rate due to thyroid cancer did not decrease despite the resection of a large number of small thyroid cancers in South Korea also support this assumption.
Q4 Will early detection of thyroid cancer by ultrasonography improve the subsequent clinical course?
A4 The benefits of early diagnosis by thyroid ultrasonography have not been proven.There is currently no evidence to suggest that the early detection of thyroid cancer by ultrasonography improves the subsequent course in young people. On the other hand, thyroid ultrasound examination may lead to unnecessary treatment due to overdiagnosis. So in medical guidelines in some countries, follow-up with ultrasonography is not actively recommended for even children exposed to radiation. The International Organization for Cancer Research (IARC), a WHO affiliate, has issued recommendations that recommend against the population-based thyroid screening after a nuclear accident.
Q5 Is it possible to identify overdiagnosed cases individually?
A5 It is often difficult to make a judgment on individual casesOverdiagnosis can only be determined by observing the population and evaluating it epidemiologically. If an individual case is overdiagnosed or not cannot be established unless the patient is already symptomatic. It is impossible to judge by ultrasonography or cytology. Also, if surgery is performed before symptoms appear, it is not possible to decide by pathological diagnosis.
Q6 Would it be possible to avoid overdiagnosis by not having a fine- needle aspiration cytology if the tumor was small?
A6 It may reduce the chance of overdiagnosis, but its effectiveness is limited.Since 2000, the number of thyroid ultrasound examinations has increased in South Korea, resulting in a 15-fold increase in the incidence of thyroid cancer among women. About half of the surgical cases had a cancer size of 5 mm or more. So even if a nodule of 5 mm or less had not subjected to cytology, the morbidity rate would have increased eightfold. It shows that even a nodule of 5 mm or more causes a lot of overdiagnosis. Limiting the indication for fine-needle aspiration cytology might reduce the chance of overdiagnosis, but its effect is limited. Also, when young people are told that they might have a malignant tumor, it is difficult for them to decide not to proceed to a more detailed examination, however small it is.
Q7 Can I avoid overdiagnosis if I was diagnosed and treated according to the guidelines issued by academic societies?
A7 We are not sure about the outcomes for young people.The guidelines for the diagnosis and treatment of thyroid cancer have been issued by various academic societies in Japan. However, these are mainly based on the evidence of adults aged 30 and over. It is not possible to judge whether a medical decision based on them is appropriate for young people, especially children.
Q8 Suppose a child with a small thyroid cancer exhibits metastasis or recurrence. Can we be sure that he/she is not an overdiagnosed case?
A8 We cannot deny the possibility of overdiagnosis even in such a case.Many small thyroid cancers found on ultrasonography at an early age are known to last a lifetime without symptoms. However, metastasis is found in most such cases when they are examined by surgery. According to the data from the US, the recurrence rate of small thyroid cancers in children after surgery has increased significantly since the introduction of ultrasonography and early diagnosis and surgery (Hay ID et al, World J Surg 42:329-342, 2018). There is a possibility that diagnosis and treatment at an early stage may somewhat lead to an increase in the recurrence rate. These findings indicate that, in children and adolescents, it is difficult to deny that the thyroid cancer may have been overdiagnosed even when metastasis or recurrence is observed.