Introduction

In recent years, the incidence of thyroid cancer has increased worldwide, with a higher frequency in women^1-4. Some risk factors postulated for this increase are greater exposure to radiation during medical procedures⁵, obesity⁶, diet, and environmental factors⁷.

Thyroid cancer, considered one of the most frequent malignant tumors of the endocrine system, accounts for 80%-90% of cases. The most common histological type observed in most studies is papillary cancer⁸. Differentiated tumors have the best survival, especially if the tumor is small and localized; currently, 97% of patients survive for 10 years⁹.

According to several studies, the increase in the incidence of thyroid cancer may be due to overdiagnosis¹⁰⁾ or by 50% in the identification of intrathyroid papillary microadenomas due to improvements in the use of diagnostic tests and medical care¹¹.

Currently, there is an increase in thyroid cancer, and at the same time, it is being discussed whether this increase is due to overdiagnosis, which implies overtreatment¹². In Paraguay, there is no national cancer registry, and its incidence has not yet been established. The objective of this study was to describe the frequency of thyroid cancer in a specialized center for the surgical resolution of thyroid gland problems in Paraguay, focusing on age, sex, and histological type of tumors.

Methods

This was an observational, descriptive, cross-sectional, retrospective study. Data were obtained from the medical records and pathological anatomy reports of the patients of the Otorhinolaryngology Department of the Hospital de Clínicas during the period 2018-2022. The patients included in the study underwent total thyroidectomy. To determine the type of cancer, pathology reports were analyzed to confirm the presence of one of the following diagnoses: papillary, follicular, Hurthle cell, medullary, poorly differentiated, anaplastic thyroid, or thyroid cancer not otherwise specified.

Data were analyzed using SPSS v25. Qualitative variables such as sex, pathological diagnosis, and type of cancer were analyzed using frequencies and percentages, and numerical variables such as age were summarized in the central tendency and dispersion data.

Results

The observed frequency of cancer in the Otorhinolaryngology Department of the Hospital de Clínicas during the period 2018-2022 was 48.1% (95% CI: 42.31-53.9). The mean age of the cancer patients was 42.4±13.9 years. A higher frequency was observed in females 34.2%, n=89) and in those aged 25-44 years 20.0%, n=52) (Table 1).

Table 1 Frequencies of thyroid cancer according to gender and age (n=260). 

Table 2 describes the final diagnoses of the patients undergoing total thyroidectomy. Benign tumors represented 38.5%, malignant tumors 42.3%, and other types 19.2%. The most frequent diagnosis was benign tumor 38.5% (n=100) more frequent in women 34.6% (n=90), which was more frequent in women 28.8% (n=75), followed in frequency by papillary cancer 36.9% (n=96). Table 3 shows that benign tumors were more frequent in people aged-45-64 years 20.8%, n=54), and malignant follicular type tumors were more frequent in people aged 25-44 years 17.7%, n =46).

Table 2 Frequency of final diagnoses according to sex in patients undergoing total thyroidectomy (n=260). 

Table 3 Frequency of final diagnoses according to age of patients undergoing total thyroidectomy (n=260). 

Discussion

This study shows that the incidence of thyroid cancer is high (42.3%), much higher than that reported in other studies, because the sample included patients who had thyroid pathology for which they underwent thyroidectomy. Palmero et al. reported that the incidence of thyroid cancer is 6.77 new cases per 100,000 inhabitants per year, with a higher frequency in women¹³. Diaz-Soto et al., report in a similar study that the incidence rate is 25.7 per 100,000 people per year in women and 2.3 to 7.1 per 100,000 inhabitants per year in men¹⁴. The higher frequency observed in other studies was also determined in this study, women are the ones who have a greater tendency to this cancer 84.3% compared to men 15.7%.

The observed trend of the most frequent thyroid cancer was benign histological type (38.5%), which was more frequent in women. Papillary cancer was the most frequent (36.9%), followed by the follicular (2.7%) and medullary (1.5%) types. As in other studies, the most common histological type is low-risk papillary tumors, which have an excellent prognosis and important clinical implications for the management of these patients.

A higher frequency of thyroid cancer has also been observed in women and older age groups. Similarly, Cohen et al. determined a higher frequency in women (83.8%) than in men (16.2%)¹⁵. The mean age was also similar to that observed in this study (43 years), with the highest incidence between 40-49 years for both sexes¹⁵. In this study, the mean age of the patients was 42 years, and it was more frequent in women.

The higher incidence of this cancer in women may be related to hormonal factors¹⁵. According to the histological types, Cohen et al. determined that the most frequent is papillary thyroid carcinoma 90.8%, follicular 3.5%, medullary 3.1%, mixed 1.3% and anaplastic 1.3%¹⁵. Papillary carcinoma was the most frequently diagnosed carcinoma in the sample analyzed in this study (36.9%).

The data showed a higher frequency of thyroid cancer among older people. In fact, the data are consistent with studies that show that the frequency of thyroid cancer is higher among those aged 25-64 years¹⁶. One of the most common histological types is papillary¹⁷, and differentiated thyroid carcinoma is the most common, including papillary and follicular carcinomas, which represent 80% and 90% of all thyroid cancers, respectively¹⁸. Similarly, Palmero et al., in Argentina found that the most frequent histological type is papillary thyroid carcinoma 98.7%, followed by metastatic lymphadenopathy 22.9%, multifocal 36.9% with 80.2% in women¹³.

The determination of the histological type of thyroid cancer leads to a search for the causes that determine this greater frequency to investigate the risk and etiological factors of this disease. Currently, improvements in diagnostic techniques and the more frequent use of ultrasound at the neck level have allowed a better diagnosis of this disease, especially in asymptomatic patients¹⁹. Overdiagnosis, understood as the detection of a disease that was never intended to affect a person during their lifetime, can be a problem because patients may be harmed by treatment, not helped, because treatment was not necessary²⁰.

The increase in thyroid cancer is a trend that has been maintained in most studies; for example, from 4.9 per 100 000 people per year observed in 1975 to 14.63% per 100 000 people per year in 2016². Some reasons that have been proposed for this increase are controversial; some authors suggest that it is due to an increase in medical controls and the use of ultrasonography. However, other causes may include changes in lifestyle, radiation exposure, increasing obesity in the population, low iodine intake, heredity, and other environmental factors.

Studies of this type are important, especially for surgeons to understand the evolution of most cancers of the thyroid gland and for making clinical decisions regarding the management of thyroid cancer, which includes the extension of surgery for lobectomy or total thyroidectomy²¹. Other implications derived from these data are the determination and organization of specialized departments for postsurgical management, in which the time that patients should take thyroid hormone supplements and the monitoring time to prevent complications should be analyzed.

The increase in thyroid cancer observed in some studies may be due to overdiagnosis of clinically asymptomatic thyroid cancer²². However, the incidence of thyroid cancer is increasing. Although no increase in anaplastic thyroid cancer has been observed in other studies, timely action is necessary due to the high morbidity and mortality²³. Differentiated thyroid carcinomas are mainly treated with surgery and radioactive iodine, and they have a good prognosis with adequate clinical and surgical management²⁴.

Some limitations of this study are that the incidence of cancer was observed in patients who underwent total thyroidectomy, which excluded patients who underwent lobectomies or other minor procedures. Similarly, aggressive thyroid cancer types were grouped into three subgroups, which may have been different if classified according to cancer staging. Another limitation is that the data cannot be generalized to the general population because it is from a specialty clinic, which determines a higher frequency than that observed in other population studies. Unfortunately, tumor size was not systematically collected from patient databases.