Nodulous pathology in members of the Ukrainian-American Thyroid Cohort: a descriptive analysis of cases first detected in 2-4 screening cycles

Abstract

Abstract. The detection of thyroid nodules is becoming increasingly common in clinical practice worldwide. The vast majority of neoplasms are benign; thyroid cancer is diagnosed in approximately 4.0-6.5% of cases. Risk factors for thyroid cancer and nodular pathology are under intense study. Radiation exposure is one of the most well-documented risk factors for thyroid cancer. There is much less evidence for a link between childhood radiation exposure and thyroid nodules. As part of the «Scientific Project to Study Cancer and Other Thyroid Diseases in Ukraine as a Result of the Chornobyl Accident» jointly with the National Cancer Institute (USA), a cohort of 13,243 individuals exposed to radiation at the age of <18 years was created, and followed for 25 years. At the first screening, thyroid nodules were diagnosed in 366 individuals, which was 2.8% of all those examined.

The aim: descriptive analysis of thyroid nodules, first detected in Project participants in the following (2-4) screening cycles.

Material and methods. The analysis included the results of 3 screening cycles of Project participants: the 2nd (2001-2003), 3rd (2003-2005) and 4th (2005-2008). A group of 1109 people with newly detected thyroid nodules ≥5 mm in size was formed: 328 people (2nd cycle), 394 (3rd) and 387 (4th). The age of the subjects at the time of the Chornobyl accident was 0-18 years, at the time of detection of nodal pathology – 15-38 years. An analysis of demographic data, as well as the results of ultrasonography (number and size of nodes) and laboratory determination of the content of thyroid stimulating hormone (TSH), free thyroxine (FT4), thyroglobulin (TG), antibodies to thyroid peroxidase (ATPO) and anti-thyroglobulin аutoantibodies (ATTG) was carried out.

Results. Two-thirds of individuals with thyroid nodules were female. The age distribution of the group at the time of the accident was as follows: ≤4 years – 27.9%, 5-9 years – 25.2%, 10-14 years – 37.0%, and ≥15 years – 9.9%; by radiation dose (Gy): <0.3 – 58.6%, 0.3-1.0 – 21.6%, and >1.0 – 19.8%. The newly detected nodules were predominantly solitary (74.7%) and had a small (5-9 mm) size (73.0%). Almost all individuals (more than 90%) had functional thyroid parameters within the reference values at the time of nodule detection. The incidence rates of nodular goiter among the Project participants based on the results of 2-4 screening cycles (2001-2008) were 12.7-17.8 cases per 1000 person-years, which is 20-30 times higher than the data for the population of Ukraine as a whole in the corresponding period. At the same time, the incidence rates in each subsequent screening cycles were higher than the calculations for the previous survey period.

Conclusion. A significant increase in the number of single small nodules among newly detected nodular formations in Project participants over the 2nd to 4th cycles of screening is apparently a consequence of frequent examinations (every 2-3 years) and indicates its effectiveness. High rates of nodular goiter incidence among Project participants may be associated with the effect of regular screening, mild to moderate iodine deficiency in the northern regions of Ukraine, and radiation exposure as a results of the Chornobyl accident. Given the increasing trend in the incidence of nodular goiter among individuals with a history of childhood radiation exposure, maintaining the Project cohort and its subsequent monitoring is extremely important.