By far, thyroid carcinoma is the most common type of endocrine cancer.1,2 Papillary carcinoma (PC) is the most common subtype of thyroid carcinoma. Although malignant neoplasms of the thyroid correspond to only 1% of all cancers and to 0.5% of all deaths caused by cancer in the world,3,4 autopsy studies have shown that PC is extremely common and underdiagnosed. One of the best-conducted studies from a methodological point of view was that by Harack et al. In their paper, these authors analyzed 101 glands sectioned at 2–3mm intervals. Neoplastic foci were found in 36% of cases, all in individuals with no prior knowledge of thyroid pathology. In most cases the tumors were represented by small microcarcinomas, and many others may have been lost, solely due to the predetermined interval section.5

Although thyroid PC is a disease of low mortality,6,7 it still remains a cause of concern. The growing incidence of a disease with a high cure rate increased its prevalence rates, resulting in significant financial impact on society.8 An epidemiological review among US individuals revealed that the incidence of thyroid cancer has increased more than twice in the last 30 years, making it the tumor with most pronounced increase in incidence between the years 1992 and 2002.9

Most studies have attributed this increased incidence to the greater use and better quality of diagnostic tools, which could lead to an increase of incidental diagnoses of previously hidden carcinomas.10 Other studies have produced results opposed to this hypothesis, as they also showed an increase in the incidence of tumors larger than 1cm, leading their authors to believe that this increased incidence may also be occurring among tumors that were not diagnosed occasionally.11 These results are based on inferences from data from preoperative cytological studies and from tumor diameters. Although to date there is no strong evidence of a global and uniform increase in exposure to risk factors historically known for this disease, it still remains uncertain whether the increase of new cases of thyroid cancer reflects a higher risk of developing this neoplasia, or whether this is only an artificial result related to diagnostic procedures.

A great number of international studies are based on regional or national statistics. Only a few institutional papers studied features associated with the diagnosis process, and none of them with a qualitative approach. The authors’ aim was to analyze the pattern of occurrence of thyroid cancer over a decade, in a quantitative and qualitative documentary study based on an institutional historical series, with a detailed description of clinical, epidemiological, and histopathological data, and with information regarding the diagnostic process for nodules and cancers.

The increased incidence of thyroid cancer in the last two decades has been observed in several studies.16–20 Few studies in Brazil analyzed incidence variations in thyroid carcinoma.21,22 Data from various regions of the world have shown an increasing incidence, from 60% to 90%, or even more. Although the present data are based on a single center, this study also observed an increase in the occurrence of thyroid cancer over the years, in proportion to the total number of thyroidectomy procedures performed, a finding which is in line with other institutional series.17,18

Just as observed by other authors,23,24 the proportion of small tumors (<1cm) increased dramatically over the past years in this sample. There was a predominance of histopathological features of low tumor aggressiveness among newly diagnosed cases, suggesting the establishment of earlier diagnoses. In the literature, there is still an ongoing discussion about the reasons for this phenomenon. There is no way to infer the level of impact of each factor on changes in the pattern of disease occurrence. Many studies have related the variations in incidence with the increased use and to the better accuracy of diagnostic tools,16 which would lead to an increase of new cases of incidental diagnosis. However, the parameters for definition of a carcinoma as an incidental event vary significantly. Some studies use the criterion “lack of suspicious or confirmatory cytological results for malignancy”25; others use the incidental finding of cancer in thyroidectomy procedures for multinodular goiter,10 and finally others are based on a nodule found occasionally in imaging studies performed for other causes.26 Most studies do not consider clinical and ultrasonographic data analysis, neither differentiate cases with an incidental diagnosis of nodule vs. cancer. Such information is difficult to measure and may be accessed solely by studies with a qualitative approach.

Some studies support their findings on inferences from preoperative cytology and tumor diameter data. Even among these studies, it is recognized that a review of those clinical circumstances that led to the identification and therapeutic decision in each case should be conducted, with the aim to verify the rate of incidental diagnosis.11 Case studies with an incidental diagnosis of cancer on imaging studies, such as that by Shetty et al.,27 show that the presence of new diagnoses of nodule or cancer among patients with tumors with diameters greater than 1cm does not exclude the possibility that many of these cases may have been diagnosed occasionally.

Burgess et al. analyzed the change in incidence of thyroid cancer in Tasmania between 1988 and 1998. These authors observed an increase in the use of FNA in the preoperative period in patients undergoing thyroidectomy, both for tumors greater than or equal to 1cm, and for tumors less than 1cm; this suggests that more cases are being treated by surgery, thanks to the preoperative suspicion of malignancy, even among patients with microcarcinomas.11 Sosa et al. observed that in the United States, the use of FNAB more than doubled in a period of five years.28 Similar results were found by Busco et al. in Italy.29 In the present study, although no statistically significant differences were found when comparing units and subunits between the two halves of the decade, it was observed that not only is FNAB an increasingly used method in the preoperative period of patients with thyroid nodules, but also that there was a trend for surgical treatment of new cases of microcarcinomas with strong suspicion or cytological confirmation of malignancy. Patients with microcarcinomas diagnosed by cytology in the preoperative period represent an increasing group among the new cases that have been diagnosed, probably reflecting improved accuracy of diagnostic methods.

In 1993 Martinez et al. observed a relationship between histopathological analysis method and frequency of diagnoses of microcarcinoma.30 According to reports of the present pathologists’ group, the number of histological sections in each surgical specimen has also increased over the years, although the annotation of section thickness in the histopathological report is not routinely performed in all cases. Even the American College of Pathologists (ACP) protocols31 do not mention a section thickness that must be routinely used–a fact that, as is well known, can influence the incidence of occult tumors. Most of the information related to histopathological analysis methods is based on indirect results. In a study by Haymart et al., a higher percentage of incidental microcarcinoma detections was found among patients undergoing surgery for follicular neoplasms, compared to other benign conditions (9% vs. 6%, respectively).25 Similarly, an increasing rate of carcinomas associated with follicular lesions was also observed, when the two halves of the decade were compared, although without statistical significance. Usually, a greater number of histological sections are carried out to differentiate benign follicular lesions vs. carcinomas with a follicular pattern. It was also noted that the mean diameter of the nodules was significantly different among patients with associated follicular lesions and with glands without other features, except for the presence of cancer. Similarly, in the qualitative analysis phase, a rising group represented by patients operated for goiter or ecographically suspicious nodules was noted, with or without previous FNAB, showing follicular lesions or Hashimoto's thyroiditis in nodular form, associated with the presence of microcarcinomas incidentally diagnosed in histological sections.

Based on these results, the authors cannot suggest another reason for the changes in pattern of occurrence observed besides those related to medical behavior, and to the accuracy and dissemination of diagnostic methods. It would be unlikely to observe an increase in the occurrence of disease in such a short period of time, if were not for a relationship to medical practices or to any change in institutional policies, with reference to surgical services in this hospital. The probability of cancer diagnosis among cases undergoing thyroidectomy has increased over the decade. The new cases tend to present with smaller diameters and with less aggressive characteristics. These results suggest a trend toward an earlier diagnosis of the disease, which, as it is believed, may also be related to the availability and accuracy of diagnostic methods. The authors believe that the lack of statistical significance – when the data from the qualitative phase were analyzed – is due to the losses and to the small number of analyzable cases in each unit or subunit, especially in the first half of the decade.

Other factors may have influenced the pattern of occurrence observed in this study, although it is difficult to establish how each of these findings may have affected the final result. Increasingly, the professional responsible by the surgical treatment of thyroid cancer in this institution is the head and neck surgeon. Furthermore, there is a tendency for completion of the histopathological analysis of thyroid specimens by the same pathologist, which also could interfere with variations of occurrence of tumors with borderline characteristics.

Many factors may have influenced the changes in the pattern of occurrence of thyroid cancer in this institution. An increase in the proportion of malignant neoplasms among cases undergoing thyroidectomy was found, as well as a trend to earlier diagnoses over the years of this study. It was observed that it is possible to find small-diameter nodules and neoplasias non-incidentally. Among microcarcinomas, an increase in the proportion of cases with preoperative suspicion of neoplasia was observed, suggesting a trend toward improvement in the accuracy of preoperative diagnostic methods among small tumors. Cases of incidental diagnosis of microcarcinomas in thyroidectomies for benign or indeterminate conditions are also increasingly common, suggesting changes in the analytical method and in histopathological routine. Longitudinal studies can complement these results, reducing losses by improving the quality of registration of data related to the diagnosis process.

The authors declare no conflicts of interest.