Incidence Thyroid cancer is the most common endocrine malignancy, accounting for 1.9% of new tumor cases diagnosed annually in the United States (0.92% in men; 2.9% in women). The annual incidence varies by region, age, and sex. The age-adjusted annual incidence rate in the United States from 1996 to 2000 was 68/1000000, with a higher rate in women (99/1000000) than in men (36/1000000). Some of the highest incidence rates in the world, such as Hawaii (119/1000000 for women; 45/1000000 for men), may be influenced by local environmental factors. Poland (Poland) has one of the lowest incidence rates, 14/1000000 for women and 4/1000000 for men. thyroid cancer in children under 15 years of age is rare, with an annual incidence rate of 2.2/1000000 for girls and 0.9/1000000 for boys in the U.S. The annual incidence of thyroid cancer increases with age in those aged 50-80 years, with a peak of 100/1000000 to 120/1000000. 1,000,000 to 120/1,000,000. As in other countries, the incidence of thyroid cancer in the United States has been gradually increasing over the past few decades, especially in women. For example, in Connecticut, the age-standardized annual incidence rate for women showed a progressive increase: 13/1000000 in 1935-1939, 36/1000000 in 1965-1969, 45/1000000 in 1985-1989, and 58/1000000 in 1990-1991. The corresponding figures for males were 2/1000000, 18/1000000, 21/1000000 and 26/1000000. The exact reasons for the increase in incidence remain unclear and may be related, at least partially, to the introduction of new diagnostic methods and the improvement of tumor registration systems. In the United States, the increased incidence between 1935 and 1975 may have been due to radiation treatment of the head and neck in children. However, other countries with documented increases in thyroid cancer incidence have never had radiation therapy for children routinely used, and thus other factors must be involved. In Europe, exposure to fallout from nuclear weapons experiments has been mentioned as an influencing factor, but epidemiological data suggest other, more important, influences. The incidence of thyroid cancer is no longer increasing in some countries such as Norway (Norway) and Iceland (Iceland), but continues to increase in the United States. Prevalence The prevalence of thyroid cancer varies widely depending on the region, population, and method of investigation. Mortensen et al. reported a 2.8% prevalence of thyroid cancer in 1000 consecutive routine autopsies. The high tumor prevalence is attributed to the rigorous and refined histological evaluation methods. Similar prevalence rates (2.3-2.7%) have been reported by Bici et al. and Silverberg and Vidone, but their higher prevalence is influenced by the fact that the study population was all hospitalized and is unlikely to reflect the prevalence in the general population. Small lesions (≤1 cm) of papillary thyroid carcinoma are classified as “papillary microfocal carcinoma” and are commonly seen at autopsy. Most papillary microfocal carcinomas are between 4 and 7 mm in diameter, and are further subclassified into “tiny” (5-10 mm) and “minute” (<5 mm) foci. "Occult" (occult) carcinomas have no pathological significance and should be discarded in favor of a more precise definition, as advocated by LiVolsi. Papillary microfocal carcinoma is usually diagnosed by microscopic examination of a strict section (2-3 mm) of the thyroid. Finland (Finland) reported the highest prevalence of papillary microfocal carcinoma (≤1 cm) of the thyroid (33.7%), Japan exceeded 20%, and Olmsted County, Minnesota (USA) had the lowest prevalence (5.1%). Microfocal papillary carcinoma (<5 mm) is clinically rare, but distal metastases (e.g., pulmonary metastases) from microfocal papillary carcinoma occasionally develop. The prevalence of thyroid cancer is significantly higher than the incidence rate, reflecting the number of patients who actually survive for decades or longer. Connecticut registry data indicate a prevalence rate of 677/100,000 for men and 237/100,000 for women, which are derived from clinically apparent disease and are therefore lower than many autopsy findings. Mortality The annual mortality rate for thyroid cancer is low, 5/1000000/year, indicating that most thyroid cancers have a good prognosis. mortality is lowest in those under 50 years of age and increases sharply over 50 years of age. There are 1490 deaths from thyroid cancer in the United States each year, accounting for 0.26% of all tumor deaths (0.21% for men and 0.31% for women). Although the incidence of thyroid cancer has gradually increased, the mortality rate has declined over the past 50 years... The decline in mortality has been attributed to early diagnosis, improved management, and the low incidence of undifferentiated cancer. For example, the 5-year relative survival rate for thyroid cancer increased from 80% in 1950-1954 to 96% in 1992-1999. Histologic type The relative percentage of differentiated thyroid cancers (papillary and follicular) within a certain region depends on dietary iodine intake. Papillary carcinomas are most often found in iodine-rich areas. For example, in Iceland, where iodine intake is abundant, papillary carcinoma accounted for 85% of cases from 1955 to 1984, while follicular carcinoma accounted for 15%. In iodine-deficient Germany (Germany), papillary carcinoma accounted for 35% of cases and follicular carcinoma accounted for 65% of cases from 1960 to 1975 in Baveria. In an area with endemic nodular goiter, iodine supplementation caused an increased percentage of papillary carcinomas accompanied by an improvement in life expectancy. In the United States, papillary thyroid cancer accounts for approximately 80% of cases. The peak incidence of papillary cancer is around 40 years of age and is three times more common in women than in men. Follicular carcinoma accounts for about 5-10% of cases, with a peak incidence in the 40s and 50s, and is three times more common in women than in men. Medullary carcinoma accounts for about 5-10% of thyroid cancers, of which, 80% are sporadic and 20% familial (mainly associated with MEN-II). Sporadic medullary carcinoma occurs most often at the age of 50-60 years and is 1.5 times more common in women than in men. MEN-IIa-associated medullary carcinoma is most often seen at the age of 10-20 years, while MEN-IIb-associated medullary carcinoma is most often seen at the age of about 10 years. Familial non-MEN-associated myeloid carcinoma is more common in people over 60 years of age. The incidence of familial medullary carcinoma is comparable between men and women. Other types of thyroid cancer include undifferentiated carcinoma and lymphoma. The incidence of undifferentiated thyroid cancer has recently declined, and the decline in overall thyroid cancer mortality may be one of the reasons for this. The peak incidence of undifferentiated carcinoma is at the age of 70, with a female to male ratio of 1.5:1. Lymphoma accounts for about 5% of thyroid malignancies, with a clinical average age of prevalence of 60-65 years. Lymphoma accounts for about 5% of thyroid malignancies, and the average age of prevalence is 60-65 years. Risk factors for thyroid cancer The incidence of thyroid cancer is closely related to certain risk factors: 1. The incidence rate increases with age; 2. Some studies suggest that biological changes that occur during pregnancy may increase the risk of thyroid cancer development; 3. Several common complications (e.g. Gardner syndrome, adenomatous polyposis coli, Cowden's disease) may increase the risk of thyroid cancer development; 4. Exposure is the only definite factor in the development of thyroid cancer; 5. Much evidence suggests that Hashimoto's thyroiditis has the potential to develop into thyroid lymphoma. In addition to these well-established correlations, there are a number of yet-to-be-proven putative risk factors for thyroid cancer. These include iodine deficiency and endemic nodular goiter, which may be due to long-term stimulation of thyroid tissue by elevated TSH levels. The data associated with these hypotheses are less consistent. One study in the United States, comparing the effects of nodular goiter prevalence and iodine supplementation in the evaluation of thyroid cancer, did not support the association of endemic nodular goiter with thyroid cancer. grave's disease has also been hypothesized to be associated with an increased incidence of thyroid cancer. The rationale associated with this assumption is that the thyroid gland stimulates TSH-like activity of immunoglobulins. However, the data show inconsistency, with the ratio of reported glandular tumors due to the effects of Grave's disease ranging from 0.06%] consistently high to 8.7%. Past reports have been low, with several recent reports ranging from 5.1 to 7.0%. The possibility of increased tumor risk in other benign thyroid disorders has also been considered. These data are difficult to interpret because of the great potential for examination and memory bias. Further, pathological examination of thyroid tissue is well established and it can reveal many unpredicted microscopic cancer foci of little clinical significance. However, a recent pooled analysis of 14 controlled studies provides evidence that women with a history of nodular goiter and benign nodules are at significant risk for thyroid cancer. This evidence was confirmed by the prospective Denmark study. Thus, the recent data tentatively suggest that nodular goiter and benign nodules/adenomas are the greatest risk factors for thyroid cancer, with the exception of childhood radiation.