Differentiated thyroid carcinomas (DTC) are the most frequent malignant endocrine neoplasias [
Total thyroidectomy followed by radioiodine ablation (131I), associated with TSH suppression therapy with levothyroxine, is the initial treatment recommended for the majority of patients [
Thyroid ablation by 131I fosters the followup of patients with DTC since it increases serum thyroglobulin specificity as a tumor marker. It also fosters early metastasis detection by means of whole-body scanning (WBS) after an uptake [
Recent studies have reported increased risk for developing a second cancer after radioiodine therapy [
Hence, the present study aimed at evaluating the frequency of another primary malignancy, in addition to DTC, and its temporal relation to 131I, in patients assisted at a specialized outpatient unit of a university hospital.
The medical records of 168 patients with DTC who initiated followup at the Thyroid Neoplasia Outpatient Unit of the Botucatu School of Medicine, UNESP from 1970 to 2008 were retrospectively evaluated.
The following data were obtained: gender, age, age at the time of thyroidectomy, DTC histological type, follow-up period, radioiodine therapy performance, accumulated dose of 131I, presence of a second malignancy, age at its diagnosis, temporal relationship between the diagnosis of the second malignancy and 131I dose, and the second type of malignancy presented.
Of the 168 patients, eight were not submitted to 131I, and 12 did not have information about the total 131I dose. Thus, the number of patients effectively treated with radioiodine was 148. They were classified into two groups (with and without another neoplasia after 131I use) and then compared in relation to gender, age at thyroidectomy, histological type of DTC, follow-up period, accumulated dose of 131I, age at the diagnosis of another malignancy, and the second type of malignancy presented.
The patients who developed another neoplasia were also classified into two groups: the first group showed a second malignancy before the 131I dose and the second group showed it after the 131I dose. Such two groups were also compared with respect to the abovementioned parameters.
Excel sheets (Microsoft Corporation, EUA) and the Statistical Analysis System (SAS) software package, version 9.2, were used for statistical analysis. Results were expressed in terms of frequencies, mean ± standard deviation, or median (minimum and maximum values). Clinical, laboratory, and development data were compared by using the most appropriate statistical tests to each case. Student’s
The patients’ general, clinical, epidemiological, and therapeutic characteristics, are shown in Table
Clinical, epidemiological, and therapeutic characteristics of 168 patients with differentiated thyroid carcinoma (DTC).
Clinical, epidemiological, and therapeutic characteristics | |
Females | Female: 142 (84.7) |
Age* (years) | 45.15 ± 15.32 |
Follow-up period** (months) | 77.5 (1; 468) |
Papilliferous carcinoma | 137 (81.5) |
Radioiodine therapy | 160 (95.2) |
Radioiodine dose** (mCi) | 200 (30; 870) |
Another neoplasia | 15 (8.93) |
*mean ± standard deviation; **median (minimum value; maximum value).
Clinical and epidemiological characteristics of 15 patients with differentiated thyroid carcinoma and another malignancy.
Clinical and epidemiological characteristic | Another malignancy | ||
Postiodine | Preiodine | ||
Males | 4 (57.14) | 3 (37.5) | 0.6193 |
Age at thyroidectomy (years)* | 61 ± 17 | 51 ± 13.7 | 0.2295 |
Follow-up period (months)** | 75 (48; 336) | 56.5 (20; 60) | 0.1505 |
Age at diagnosis of a second neoplasia* (years) | 69.4 ± 11.4 | 46.1 ± 20.2 | |
Classic nonpapilliferous histological type | 3 (42.85) | 2 (25) | 0.6084 |
*mean ± standard deviation; **median (minimum value; maximum value).
The neoplasias diagnosed before and after 131I therapy are specified in Table
Types of other neoplasias diagnosed in 15 patients with differentiated thyroid carcinoma.
PRE 131I | POST 131I |
---|---|
2 breast adenocarcinomas | 2 skin spinocellular carcinomas |
1 chronic myeloid leukemia | 1 prostate adenocarcinoma |
1 lymphoma | 1 colon adenocarcinoma |
1 rectal adenocarcinoma | 1 endometrial adenocarcinoma |
1 Palatal spinocellular carcinoma | 1 rectal carcinoma |
1 testicular seminoma | 1 lung carcinoma |
1 endometrial adenocarcinoma |
Of the 148 patients who received a known accumulated dose of 131I, seven (4.7%) developed a second malignancy after treatment. The median time between 131I therapy and diagnosis of second malignancy was 60 months, with minimum of 6 months and maximum of 275 months. Age at thyroidectomy was greater in the group of individuals who developed another malignancy than in those who did not show it (
Clinical, epidemiological, and therapeutic characteristics of 148 patients with differentiated thyroid carcinoma who received a therapeutic dose of radioactive iodine and showed another postiodine malignancy or not.
Clinical and epidemiological data | Another postradioactive iodine malignancy | Odds ratio | IC 95% | ||
Yes | No | ||||
Males | 4 (57.1) | 21 (14.9) | 0.123 | 0.015–1.026 | 0.0528 |
Age at thyroidectomy (years)* | |||||
Follow-up period (months)** | 75 (48; 336) | 74 (9; 468) | 1.013 | 1.000–1.026 | 0.0514 |
Accumulated dose of 131I (mCi)** | 175 (100; 300) | 200 (30; 870) | 0.994 | 0.985–1.002 | 0.1375 |
Classic nonpapilliferous histological type | 3 (42.8) | 59 (41.8) | 2.350 | 0.311–17.742 | 0.4073 |
*mean ± standard deviation; **median (minimum value; maximum value).
The association of radioiodine therapy with the development of a second neoplasia in patients with DTC has been controversial. In our service, the frequency of other primary neoplasias was 8.9%, which is an apparently high percentage when taking into account that the estimated incidence of malignant neoplasias for the general population in São Paulo state for the years 2010 and 2011 is approximately 313 per year for every 100,000 inhabitants [
Increased risk for a second neoplasia in patients with DTC has been reported. Sandeep et al. analyzed over 39,000 patients with thyroid carcinoma and observed 30% risk increase for developing a second malignancy as compared to the general population. Additionally, greater occurrence of thyroid cancer in patients with other types of neoplasias has been found [
In the present study, it was observed that, of the patients showing another neoplasia, similar percentages had (46.6%) or had not (53.3%) received a therapeutic dose of 131I before the other neoplasm. These findings are in agreement with those reported by Bhattacharyya et al., who observed that the use of radioiodine did not increase risk for developing a second neoplasia by evaluating over 29,000 patients with DTC [
Other studies, however, have shown increased risk for a second malignancy related to radioiodine therapy. In a prospective study on 6,841 European patients with DTC, Rubino et al. reported 27% risk for developing a second neoplasia, which is a significant increase in relation to the general population in the studied countries [
The differences in the findings from different studies may be related to a number of factors, among which are the particular characteristics of the studied populations. Some factors, such as genetic profile and environmental characteristics, certainly influence the prevalence of different types of cancer. The role played by genetic heredity has been particularly studied. Several loci have recently been associated with some types of cancer and reported to increase their risk [
In addition to the aforementioned factors, which affect the general population, we could question how much nutritional habits and iodine sufficiency influence the occurrence of other neoplasias, specifically in patients with DTD treated by 131I. The uptake of iodine by the thyroid tissue is mediated by sodium-iodide symporter (NIS), cloned in 1996 [
In this study, the studied characteristics (gender, follow-up period, histological type, age at diagnosis of another neoplasia) showed no statistical differences when comparing the group that developed a second malignancy before 131I use and the group that developed another neoplasia after 131I therapy. The only parameter showing significance was age at diagnosis of another neoplasia.
When comparing the patients who underwent radioiodine therapy but did not develop a second neoplasia (141) to those who were also submitted to 131I and later developed another malignancy (7), again no differences were found for the following studied parameters: gender, follow-up period, histological type, and accumulated 131I dose. Additionally, the median accumulated 131I dose in patients who did not develop a second neoplasia (200 mCi) was even higher in relation to those showing another malignancy (175 mCi). The only parameter that showed statistically significant differences was age at thyroidectomy, thus suggesting that older patients at the time of surgery could be at increased risk for developing a second malignancy. The causes for this finding remain to be clarified. With respect to other primary malignancies found, no predominance of any specific neoplasia was observed.
Our study showed limitations, such as its retrospective character and a short follow-up period (approximately 6.5 years). Moreover, we did not do an active screening of other cancers, considering the retrospective nature of the study, such a procedure impractical to monitor all patients with differentiated thyroid cancer, which would burden our health system. Nevertheless, our findings, as previously described in other studies, can suggest that, at least in certain populations, the occurrence of another malignancy after 131I does not have a causal relationship with such treatment. Hence, patients with DTC could have increased incidence of a second neoplasia which is not related to 131I therapy, thus more probably suggesting a common etiology and/or a genetic mechanism rather than a causal relationship between the two tumors.
The authors declare that there is no conflict of interests.