6 March 2019 There are 2 types of endocrine cells (hormone-producing cells) in the thyroid: Follicular cells — which produce T4 and T3 hormones; C Cells — which produce calcitonin. Papillary carcinoma and follicular carcinoma originate in follicular cells and account for around 85% of malignant thyroid tumours. They are also known as differentiated carcinomas of follicular origin. Undifferentiated, medullary (originating in the C-cell) and anaplastic thyroid cancers are much less frequent. How is thyroid cancer diagnosed? Thyroid cancer is almost always diagnosed after investigation of a painless nodule on the thyroid. There are several signs and symptoms that can raise suspicion a thyroid nodule is malignant; however, these are by no means definitive: Progressive growth; Hoarseness; Hardness of the nodule; Lymph nodes increased in size. Fine-needle aspiration cytology enables medical staff to get closer to a final diagnosis. However, even a malignancy diagnosed by this method still requires confirmation, which involves looking at the entire nodule under the microscope (histological examination) after surgery . How is thyroid cancer treated? There are three main approaches to the treatment of papillary and thyroid follicular cancers: Surgery: when cancer is diagnosed, the entire thyroid should be surgically removed (total thyroidectomy). The surgery may also include the lymph nodes in the neck if they are affected by the disease; Radioactive iodine (Iodine-131): the administration of radioactive iodine is a form of radiotherapy that selectively affects malignant tumours originating in follicular cells (papillary, follicular and undifferentiated cancers). In this way, tissues and organs not affected by the disease are saved; Thyroid hormone: in many cases, thyroxine should be administered at a dose that allows the pituitary gland to suppress thyroid stimulating hormone (TSH) production. This hormone stimulates the multiplication of malignant thyroid cells that may not have been eliminated by the surgery. Radioactive iodine treatment The level of activity of the iodine used to treat thyroid cancer is several times greater than that used to treat hyperthyroidism. This means treatment has to be carried out in hospital under special conditions. The main objective of carrying out treatment in hospital is to protect the community from radiation emitted by iodine-131. In most cases, only one treatment is needed. If it needs to be repeated, there should be an interval of 4 to 6 months between treatments. There is no predefined limit for the maximum number of treatments to be carried out. Everything depends on the specific clinical characteristics of each situation. Thyroid follicular cells produce T4 and T3 hormones, which have iodine in their composition. These cells, therefore, have an unusual feature among the cells in our body: they capture and store the iodine dissolved in the blood. Treatment with radioactive iodine can have 2 objectives: To prevent the reappearance of the disease: In this situation, treatment is said to be ablative. People who are at greater risk of relapse due to their age or the characteristics of their tumour undergo this treatment. This treatment also makes it possible to optimise future clinical surveillance; To destroy tumour tissue that could not be removed during surgery. Iodine-131 treatment can be performed after a total thyroidectomy, i.e. after total removal of the thyroid. Increased thyroid stimulating hormone (TSH) in the blood greatly increases the effectiveness of treatment with radioactive iodine. Increased TSH levels can be achieved in 2 ways: Inducing a state of hypothyroidism: by suspending habitual treatment with thyroxin hormone. This is the oldest form of preparation for treatment. However, this form of preparation is not always indicated; Administering human TSH by injection: with this more modern method, it is possible to avoid the symptoms of hypothyroidism (tiredness, slowed thought processes, reduced concentration and swelling, among others) and reduce the exposure of the rest of the body to radiation. Another way of increasing the efficacy of the treatment is to restrict contact and ingestion of products that are rich in iodine. In this way, the thyroid cells capture the radioactive iodine more efficiently. Side effects Treatment with radioactive iodine is very safe and well tolerated by most people. The most commonly reported side effects are: Changes in sense of taste; Nausea; Neck pain or swelling (when this occurs, it is usually mild); Inflammation of the salivary glands: lemonade and chewing gum are recommended to mitigate this risk while in hospital. Large amounts of water should also be consumed while in hospital so the body can eliminate the radioactive iodine as quickly as possible. The most serious complications associated with radioactive iodine treatment will only arise if multiple treatments are needed. Staging of the disease After treatment with radioactive iodine a full-body scan is performed. This examination will show the areas of the body where radioactive iodine has been taken up. Where this has taken place outside of the usual thyroid location, it may be an indicator of the existence of metastases (thyroid cells outside of their natural location). These cases are uncommon in the most frequent forms of thyroid cancer. Care after discharge After hospital discharge, it is almost always necessary to take some care with a view to reducing the exposure of the community to radiation. Particular care should be taken with regard to contact with pregnant women and children under 10 years of age. What happens after treatment? After the initial treatment (surgery and possibly radioactive iodine), people with differentiated thyroid cancer of follicular origin should be monitored periodically. Follow-up should take place for some time, as it is possible for the disease to reoccur even years after diagnosis and initial treatment. In monitoring these patients, the following are of particular importance: Clinical evaluation carried out at each visit: cervical palpation is a fundamental part of this examination; Determination of thyroglobulin levels: thyroglobulin is a molecule produced only by the thyroid, and which is associated with the storage of hormones in this gland. After thyroidectomy and treatment with radioactive iodine, if there are no malignant cells, the level of thyroglobulin in the blood will in most cases be undetectable. If it reappears or its levels increase, this is most likely to be associated with a relapse or progression of the disease; Neck ultrasound: a painless and harmless examination that allows the discovery of malignant lesions measuring less than 0.5 cm. Thyroid papillary and follicular cancers, when appropriately treated, have an excellent prognosis. Survival rates are in the order of 95% at 10 years after diagnosis. This article was written with the support of physicians and other clinical professionals from the Hospital da Luz network. The content published in the Health Guide is intended for the general public and is provided for informational and educational purposes only. It does not replace individual medical assessment, diagnosis, or personalized clinical advice from a qualified healthcare professional. The content is produced or reviewed by physicians and other healthcare professionals at Hospital da Luz and is based on the knowledge available at the time of publication or the most recent update, as indicated at the beginning of each item.
