Thyroid Cancer â South American Experience

Abstract

Thyroid cancer comprises a broad spectrum of diseases with variable prognoses. The diagnosis of thyroid cancer usually follows the identification of a thyroid nodule on physical examination or as an incidental finding on diagnostic imaging performed for other reasons. It is considered the most frequent endocrine cancer, and its incidence has been growing steadily during the past three decades around the world. This trend is a constant in every continent except for Africa. Thyroid cancer is the fifth most common malignancy among women and its incidence has only declined in a few countries. The incidence of thyroid cancer may be substantially different around the world, and the potential causes are related to racial, ethnic and geographical differences or to environmental differences such as excessive or deficient iodine, in addition to radiation exposure. Thyroid cancer is the sixteenth most frequent malignancy around the world, with approximately 298,000 new cases diagnosed in 2012 (2% of the total). Thyroid cancer increase has been associated to socioeconomic status, better access to healthcare and rising use of thyroid imaging. Therefore, the rise could be apparent because of the useless identification of a large reservoir of subclinical papillary lesions that will never affect patient health (over diagnosis). Although increased detection might have played a major role, some evidences suggest that true increase in incidence have also contributed to such phenomenon. The evidence indicates that the type of thyroid cancer that has experienced a substantial increase in terms of frequency is papillary cancer, with no significant changes in the frequency of the other types of cancer and histological variants. Though the increased frequency is the same for all tumor sizes, it is more evident in <1 cm tumors (micro carcinomas). However, it is also true that the information derived from tumor histology is now more accurate and complete, reducing the number of the so-called unspecific/unknown categories. The information available for South America – except for a few countries – is limited and scattered; in countries like Brazil, Chile and Colombia the population coverage is insufficient to ensure reliable data and complete cancer records; moreover, there are no universal criteria to ensure data collection from most of the population. Though there is comprehensive information about specific populations or geographical areas, the real situation regarding thyroid cancer in the population is unknown. However, the creation of population-based cancer records has led to a more accurate vision of the problem. The objective of this review is to provide an update on the epidemiology of thyroid cancer in South America; discussing the probable causes that have led to increase in frequency in the population, for this purpose we conducted a systematic medical literature review (see “Literature search”). We find that in South America few cancer registries are based on the population; countries like Chile have sub-registries and this results in an underestimation of thyroid cancer due to an incomplete registry of cases because some of the pathologic anatomy centers failed to participate in the trial; similarly, Brazil evidences an under-registration of thyroid cancer, as a result of the difficulties to access healthcare services and of the quality of the data in the available registries. The national cancer information system has not yet been implemented in Colombia, and reporting malignant neoplasms is not obligatory, except for neoplasms present in the pediatric population.