Will long-term consumption of iodized salt lead to thyroid cancer? The answer is…

Author: Zhang Bin, Chief Physician, Peking University Cancer Hospital

Chairman of the Head and Neck Tumor Committee of the Tumor Branch of the Chinese Medical Doctor Association

Reviewer: Li Guangwei, Chief Physician, Fuwai Hospital, Chinese Academy of Medical Sciences

Vice Chairman of the Chinese Medical Association Endocrinology Society

Data from the National Cancer Registry Center show that the number of thyroid cancer patients in my country continues to grow at a rate of 20% per year. Thyroid cancer has become one of the major cancers that threaten human health.

What causes thyroid cancer? Is it related to eating iodized salt? Are thyroid nodules a precursor to thyroid cancer? Can thyroid cancer be detected early? Let's talk about related issues today.

1. What causes thyroid cancer?

According to the pathological type of thyroid cancer, it can be divided into four categories. Different types of thyroid cancer have different causes.

The most common type is papillary thyroid cancer. If not specified, thyroid cancer generally refers to papillary thyroid cancer, because this type of thyroid cancer accounts for more than 90% of all thyroid cancers, and can even account for 95%.

The second type is follicular thyroid carcinoma, the third type is medullary thyroid carcinoma, and the last type is anaplastic thyroid carcinoma, which has a very low incidence but a very high degree of malignancy.

For papillary thyroid cancer, the cause of its occurrence is relatively clear, and the most important one is ionizing radiation.

Figure 1 Original copyright image, no permission to reprint

Speaking of ionizing radiation, some friends may ask, can mobile phones cause thyroid cancer? Can microwave ovens cause thyroid cancer? No. Because they are all non-ionizing radiation, which are electromagnetic waves with relatively low energy. Only ionizing radiation such as X-rays and gamma rays can cause thyroid cancer.

Of course, there are also some other related factors, such as obesity, genetics, female hormones, and benign thyroid lesions.

For medullary thyroid cancer, its cause has little to do with ionizing radiation and is more related to genetics. Approximately 20% of patients have genetic disease.

The clear cause of undifferentiated carcinoma has not yet been found, but undifferentiated carcinoma is mostly transformed from papillary carcinoma.

Many people have a misunderstanding that thyroid cancer is related to iodized salt. In fact, there is no relationship between the two, so you don’t need to worry about eating iodized salt.

2. Are thyroid nodules a precursor to thyroid cancer?

Thyroid nodules and thyroid cancer are two different concepts.

Thyroid nodules are found in the thyroid gland by clinical palpation or ultrasound. We call them thyroid nodules if their nature is uncertain. If they are malignant, we call them thyroid cancer.

What is the proportion of thyroid nodules? Studies have found that among the normal population, about 1/4 of the people have thyroid nodules, most of which are benign, and the proportion of malignant nodules is very low, accounting for 6%-8%.

Many people worry that if benign thyroid nodules are not removed in time, will they turn into cancer in the future? You can rest assured about this, because whether it is from epidemiological surveys or the latest genetic research, thyroid cancer is cancer from the beginning. Benign thyroid nodules will not turn into cancer, so you don't have to worry.

Of course, there are also many patients who have benign thyroid nodules and thyroid cancer at the same time, and this ratio is still not low. But benign nodules are not precancerous lesions.

3. Can thyroid cancer be detected early?

The most common symptom of thyroid cancer is a lump in the front of the neck that moves up and down with swallowing. Occasionally, symptoms such as hoarseness or even difficulty breathing may occur.

But in the early and even middle stages of the disease, patients feel almost nothing. Even if they touch something growing on their neck, it may not hurt or itch.

Most people discover thyroid nodules during routine physical examinations. Ultrasound can be used to initially determine whether the nodule is cancerous based on its shape. If it is cancerous and its diameter is greater than 1 cm, doctors will generally recommend fine needle aspiration under ultrasound guidance, and cytopathology examination to finally confirm whether it is cancerous.

Figure 2 Original copyright image, no permission to reprint

If it is confirmed to be papillary thyroid cancer, but its diameter does not exceed 1 cm, it is considered a microcancer. In foreign countries, most people are not in a hurry to undergo surgery. If the doctor assesses it as a low risk, it can be observed regularly. This is because most microcancers remain "inert" for a long time without any changes, and can even be carried for life.

However, if the diameter of the thyroid cancer is larger than 1 cm, or if it becomes significantly larger or the lymph nodes become abnormally swollen during observation, surgical treatment should be actively performed to prevent metastasis and spread.