Incidence of Nonthyroidal Primary Malignancy and the Association with (131)I Treatment in Patients with Differentiated Thyroid Cancer

Histopathological changes in salivary glands after radioactive iodine treatment for thyroid diseases

OBJECTIVES

We aimed to evaluate the histopathological alterations in human salivary glands after radioactive iodine (RAI) treatment for thyroid diseases.

STUDY DESIGN

We retrospectively selected patients with a history of RAI treatment for thyroid diseases from a database of patients who underwent surgery for oral and maxillofacial diseases and had specimens of salivary glands at Peking University School of Stomatology between December 2012 and July 2023. The patients' clinical records and histopathological slides of the salivary glands were carefully reviewed.

RESULTS

Sixteen patients were included. Three symptomatic patients showed duct cell cytoplasmic vacuolization and increased numbers of disordered duct cell layers (3/3), severe duct stenosis and dilation (2/3), and exfoliated epithelial cells in the duct lumen (1/3). The glandular parenchyma showed severe acinar atrophy (2/2), fat content enhancement (2/2), and severe periductal fibrosis (3/3). Thirteen asymptomatic patients showed duct cell cytoplasmic vacuolization (5/13), acinar atrophy and increased fat content in the parenchyma (5/13), and periductal fibrosis (5/13).

CONCLUSION

Main histopathologic changes in the salivary glands after RAI treatment for thyroid diseases are cytoplasmic vacuolization of duct cells, acinar atrophy, fat content enhancement, and periductal fibrosis. These changes were evident in symptomatic cases, and were also seen in some asymptomatic patients.

Radioactive Iodine Therapy in Differentiated Thyroid Cancer: An Update on Dose Recommendations and Risk of Secondary Primary Malignancies

Radioactive iodine (RAI) therapy with iodine-131 is performed in select cases of differentiated thyroid cancer (DTC), typically for remnant ablation, adjuvant therapy, or treatment of known persistent disease. Herein, we review updated RAI dose recommendations and associated risks of secondary primary malignancy (SPM). RAI dose is usually chosen empirically based on the risk assessment of tumor recurrence and other factors. Dose recommendations differ slightly among relevant medical societies. As of April 2024, most medical societies, including the American Thyroid Association (ATA), European Thyroid Association (ETA), Society of Nuclear Medicine and Molecular Imaging/European Association of Nuclear Medicine (SNMMI/ EANM), and National Comprehensive Cancer Network (NCCN), recommend a dose of 1.11 GBq (30 mCi) I-131 for remnant ablation. For adjuvant therapy, the recommended RAI dose ranges from 1.11 to 3.7 GBq (30-100) mCi I-131, although doses up to 5.6 GBq (150 mCi) may also be considered. In patients with known or suspected metastatic disease, at least 3.7 GBq (100 mCi) I-131 should be administered, and RAI doses as high as 7.4 GBq (200 mCi) may be justified depending on the suspected tumor burden and extent. Dosimetry has the advantage of tailoring the RAI dose to each patient's pharmacokinetics, resulting in ≥ 7.4 GBq (200 mCi) of I-131 in most cases. There is an ongoing debate about the risk of developing SPM due to RAI therapy, with several multicenter studies and meta-analyses concerning SPM being published in the last 2 years. The incidence of RAI-associated SPM varies according to the study design and detection method. Several studies showed no increased incidence, and there was no specific secondary cancer or cancer group linked to RAI exposures. Some reports indicated that cumulative RAI doses exceeding 5.6-7.4 GBq (150-200 mCi) were found to represent an increased risk for developing SPM. However, a clearly defined dose threshold cannot be provided based on the current literature. Nonetheless, caution should be exercised when considering repeated RAI therapies for persistent metastatic PTC, with a cumulative dose exceeding 37.0 GBq (1,000 mCi), due to the potential risk of developing SPM and other long-term toxicity. Further research is warranted to understand better the relationship between RAI dose and the risk of SPM.

Risk prediction of second primary malignant tumor in primary differentiated thyroid cancer patients: a population-based study

PURPOSE

To investigate the risk factors of second primary malignant tumor (SPMT) in patients with differentiated thyroid cancer (DTC) and establish a competing risk nomogram to predict the probability of SPMT occurrence.

METHODS

We retrieved data from the Surveillance, Epidemiology, and End Results (SEER) database for patients diagnosed with DTC between 2000 and 2019. The Fine and Gray subdistribution hazard model was employed to identify SPMT risk factors in the training set and develop a competing risk nomogram. Model evaluation was performed using area under the receiver operating characteristic curve (AUC), calibration curve, and decision curve analysis (DCA).

RESULTS

A total of 112,257 eligible patients were included in the study and randomized into a training set (n = 112,256) and a validation set (n = 33,678). The cumulative incidence rate of SPMT was 15% (n = 9528). Age, sex, race, tumor multifocality, and TNM stage were independent risk factors of SPMT. The calibration plots showed good agreement between the predicted and observed SPMT risks. The 10-year AUCs of the calibration plots were 70.2 (68.7-71.6) in the training set and 70.2 (68.7-71.5) in the validation set. Moreover, DCA showed that our proposed model resulted in higher net benefits within a defined range of risk thresholds. The cumulative incidence rate of SPMT differed among risk groups, classified according to nomogram risk scores.

CONCLUSION

The competing risk nomogram developed in this study exhibits high performance in predicting the occurrence of SPMT in patients with DTC. These findings may help clinicians identify patients at distinct levels of risk of SPMT and develop corresponding clinical management strategies.

Post-Surgical Indications to Radioiodine Treatment and Potential Risk Factors for Post-Treatment Recurrence in Patients with Intermediate-Risk Differentiated Thyroid Carcinoma

In this multicentric retrospective observational study, we investigated the potential risk factors for radioiodine (RAI) indication and the post-treatment recurrence of intermediate-risk differentiated thyroid cancer (DTC) 1 and 3 years from diagnosis. We included 121 patients who underwent thyroidectomy for intermediate-risk DTC. The 92 patients (76.0%) who underwent RAI treatment had a higher prevalence of extra-thyroid micro-extension (mETE) (p = 0.03), pT3 staging (p = 0.03) and recourse to therapeutic central (p = 0.04) and lateral (p = 0.01) neck dissection, as well as higher numbers (p = 0.02) and greater dimensions (p = 0.01) of lymph node metastases, compared with untreated patients. Relapse was observed in 18.1% and 20.7% of cases 1 and 3 years from diagnosis, respectively, with no significant differences between groups. A lower age at diagnosis (p = 0.03) and higher levels of stimulated thyroglobulin (Tg) (p = 0.04) emerged as the only independent risk factors for tumour relapse at 1 year. Tumour relapse at 3 years was only independently predicted by the presence of tumour relapse at 1 year (p = 0.04). In conclusion, mETE, pT3 and the presence of large, multiple or clinically evident lymph node metastases represent the main indicators for referring patients to RAI treatment. Early recurrence may be considered the most relevant factor when planning further surveillance.

Survivorship, Quality of Life, and Transition to Adult Care for Pediatric and Adolescent Thyroid Cancer Survivors

The importance of long-term survivorship care to reduce survivor and family anxiety and burden, decrease emergency visits and health care costs, improve knowledge, as well as implement timely surveillance is widely accepted. Most childhood cancer survivors suffer from an increased number of medical and psychosocial comorbidities as they age and are at a higher risk for early mortality, which differs by cancer diagnosis. Childhood thyroid cancer survivors fall within this spectrum. Some have significant complications and/or late effects from treatment, whereas others have no long-term medical late effects, but almost all will require life-long thyroid hormone replacement therapy. Therefore, providing survivorship and transitional care, including a survivorship and/or transitional care plan (SCP/TCP), as well as periodically assessing the needs and quality of life for the patient and their family, should be implemented for our young thyroid cancer survivors.

Use of multikinase inhibitors/lenvatinib in patients with synchronous/metachronous cancers coinciding with radioactive-resistant differentiated thyroid cancer

This review focuses on patients with differentiated thyroid carcinoma (DTC) associated with multiple primary malignant neoplasm (MPMN) treated by multikinase inhibitors (MKIs) as systemic treatment for advanced disease. Despite the increasing frequency of MPMNs (many at an advanced stage) and the usefulness of MKIs for multiple metastatic cancers, published data on the management of MPMN and MKI therapies in this scenario are scarce. There are infrequent descriptions of patients with advanced MPMN treated with MKIs, but only a few have described advanced DTC. The management of MPMNs, including DTC and its particular circumstances, is reviewed, focusing on the evidence for MKI therapies. Some considerations for MPMN patients with advanced DTC are discussed, with the intention of helping physicians make decisions in these challenging situations and improving treatment and patient outcomes.

Non-thyroidal second primary malignancy in papillary thyroid cancer patients

INTRODUCTION

The occurrence of non-thyroidal second primary malignancy (NTSPM) in patients with papillary thyroid cancer (PTC) is well documented, but epidemiological data are conflicting.

OBJECTIVE

The aim of this study was to evaluate the incidence of NTSPM in a large series of patients with PTC and to assess its potential risk factors.

METHODS

Single-center cohort study with retrospective data collection conducted on consecutive PTC patients diagnosed from 1988 to 2018 with a minimum follow-up time of 2 years. NTSPM was defined as any primary malignancy with histological confirmation occurring in an anatomical site other than the thyroid. According to the timing of occurrence, NTSPM were subdivided into anachronous, synchronous or metachronous (diagnosed >6 months before, within 6 months and >6 months after PTC diagnosis, respectively).

RESULTS

We included 773 individuals (83.3% females), median age at PTC diagnosis was 47.0 (IQR: 37.0-58.0) years and median follow-up time was 9.9 (6.2-16.3) years. Incidence of NTSPM was 15.5% (n = 120) and its standard incidence ratio (SIR) was higher when compared to the general population (SIR: 2.70). Family history of malignancy and younger age at diagnosis were associated respectively with 206 and 4% increased risk of developing metachronous neoplasia (HR: 2.06 (95% CI: 1.10-3.86) and 1.04 (95% CI: 1.02-1.05), respectively).

CONCLUSION

In our series, the occurrence of NTSPM was not uncommon and its incidence was higher compared to the general population. First-degree family history of malignancy was a strong risk factor for multiple primary malignancies.

Breast metastasis of papillary thyroid carcinoma

Papillary thyroid carcinoma (PTC) is the most common type of thyroid cancer, and regional neck metastasis is more common than distant metastasis. If present, metastasis most frequently occurs in lungs and bones. Follicular variant of papillary thyroid carcinoma (FVPTC) is a mixture of the classic and follicular thyroid carcinoma and metastasizes in the same fashion as the PTC with cervical lymph nodes as the most common site. A case of atypical presentation of FVPTC with rib metastasis is reported. We present a case of an old man with a left-sided palpable breast mass for 2 months in duration without breast pain. Initially, the breast mass was categorised as Breast Imaging Reporting and Data System (BI-RADS) 4a via ultrasonography. Subsequent immunohistochemistry demonstrated that the mass was metastatic thyroid cancer. Consequently, a CT scan revealed a tumour originating from the rib. The patient was finally diagnosed with metastatic FVPTC.

Second primary malignancies induced by radioactive iodine treatment of differentiated thyroid carcinoma - a critical review and evaluation of the existing evidence

PURPOSE

Concern is growing about long-term side effects of differentiated thyroid cancer treatment, most notably radioactive iodine (RAI) therapy. However, published studies on the subject have had heterogeneous cohorts and conflicting results. This review seeks to provide an updated evaluation of published evidence, and to elucidate the risk of second primary malignancies (SPMs), especially secondary hematologic malignancies (SHMs), attributable to RAI therapy.

METHODS

An extensive literature search was performed in Ovid MEDLINE, Ovid MEDLINE and In-Process & Other Non-Indexed Citations, Ovid MEDLINE Epub Ahead of Print, Cochrane Central Register of Controlled Trials (CENTRAL) and PubMed. Studies regarding RAI-induced SPMs or a dose-response relationship between RAI therapy and SPMs were identified, 10 of which were eligible for the analysis. We evaluated risk of bias in each study and judged quality of evidence (QOE) across all studies using the Grading of Recommendations, Assessment, Development and Evaluations approach.

RESULTS

For the outcome "SPM", the relative effect (relative risk, hazard ratio, or odds ratio) of RAI vs. no RAI ranged from 1.14 to 1.84 across studies, but most results were not statistically significant. For the outcome "SHM", reported relative effects ranged from 1.30 to 2.50, with 2/3 of the studies presenting statistically significant results. In 7/8 of the studies, increased risk for SPM was shown with increasing cumulative RAI activity. QOE was "very low" regarding SPM after RAI and regarding a dose-response relationship, and "low" for SHM after RAI.

CONCLUSION

Based on low quality evidence, an excess risk for the development of SPM cannot be excluded but is expected to be small.

Association Between Radioactive Iodine Treatment for Pediatric and Young Adulthood Differentiated Thyroid Cancer and Risk of Second Primary Malignancies

PURPOSE

Since the 1980s, both the incidence of differentiated thyroid cancer (DTC) and use of radioactive iodine (RAI) treatment increased markedly. RAI has been associated with an increased risk of leukemia, but risks of second solid malignancies remain unclear. We aimed to quantify risks of second malignancies associated with RAI treatment for DTC in children and young adults, who are more susceptible than older adults to the late effects of radiation.

METHODS

Using nine US SEER cancer registries (1975-2017), we estimated relative risks (RRs) for solid and hematologic malignancies associated with RAI (yes v no or unknown) using Poisson regression among ≥ 5- and ≥ 2-year survivors of nonmetastatic DTC diagnosed before age 45 years, respectively.

RESULTS

Among 27,050 ≥ 5-year survivors (median follow-up = 15 years), RAI treatment (45%) was associated with increased risk of solid malignancies (RR = 1.23; 95% CI, 1.11 to 1.37). Risks were increased for uterine cancer (RR = 1.55; 95% CI, 1.03 to 2.32) and nonsignificantly for cancers of the salivary gland (RR = 2.15; 95% CI, 0.91 to 5.08), stomach (RR = 1.61; 95% CI, 0.70 to 3.69), lung (RR = 1.42; 95% CI, 0.97 to 2.08), and female breast (RR = 1.18; 95% CI, 0.99 to 1.40). Risks of total solid and female breast cancer, the most common cancer type, were highest among ≥ 20-year DTC survivors (RR_solid = 1.47; 95% CI, 1.24 to 1.74; RR_breast = 1.46; 95% CI, 1.10 to 1.95). Among 32,171 ≥ 2-year survivors, RAI was associated with increased risk of hematologic malignancies (RR = 1.51; 95% CI, 1.08 to 2.01), including leukemia (RR = 1.92; 95% CI, 1.04 to 3.56). We estimated that 6% of solid and 14% of hematologic malignancies in pediatric and young adult DTC survivors may be attributable to RAI.

CONCLUSION

In addition to leukemia, RAI treatment for childhood and young-adulthood DTC was associated with increased risks of several solid cancers, particularly more than 20 years after exposure, supporting the need for long-term surveillance of these patients.

Risk factors for second primary malignancies following thyroid cancer: a nationwide cohort study

OBJECTIVE

Thyroid cancer survivors have a high risk of second primary malignancies (SPMs). We aimed to evaluate the site-specific incidence, prognosis, and risk factors for metachronous SPMs following thyroid cancer.

DESIGN

A nationwide cohort study.

METHODS

This study included data from the Korea National Health Insurance Service (between 2002 and 2018). Exposure to diagnostic radiation was defined by the number of computed tomography (CT) and positron emission tomography-CT scans after the index date. A cumulative radioactive iodine (RAI) dose >100 mCi was considered high-dose RAI.

RESULTS

During the median 6 years of follow-up, among 291 640 patients, 13 083 (4.5%) developed SPMs. Thyroid cancer survivors had a 26% increased risk of SPMs compared with the general population (standardized incidence ratio: 1.26; 95% CI: 1.22-1.29). Furthermore, those with SPMs had a significantly poorer survival rate than those without SPMs (hazard ratio: 11.85; 95% CI: 11.21-12.54; P < 0.001). Significantly elevated risks were observed in myeloid leukemia and 13 solid cancer sites: lip, salivary gland, small intestine, larynx, lung, mediastinum and pleura, mesothelium, breast, corpus uteri, ovary, prostate, kidney, and bladder. Frequent diagnostic medical radiation exposure and high-dose RAI therapy were independent risk factors for several SPMs, including the cancer of salivary gland, lung, mediastinum and pleura, breast, kidney, and bladder, as well as myeloid leukemia.

CONCLUSIONS

Frequent diagnostic radiation exposure and high-dose RAI therapy are independent risk factors for SPM following thyroid cancer. Clinicians need to consider minimizing unnecessary diagnostic radiation exposure and administering a high dose RAI only when justified in patients with thyroid cancer.

Risk of Second Malignant Neoplasm in Familial Non-Medullary Thyroid Cancer Patients

INTRODUCTION

Survival rates in patients with non-medullary thyroid carcinoma (NMTC) are high, increasing the possibility to develop a second malignant neoplasm (SMN). Many studies investigated the relationship between increased risk of SMN in NMTC patients treated with radioiodine, but few data are available about the impact of family history (FH) of thyroid cancer on SMN risk.

PURPOSE

To assess the risk of SMN in a large cohort of sporadic and familial NMTC using the standardized incidence ratio (SIR).

PATIENTS AND METHODS

We studied 918 NMTC patients (73.9% female patients) followed for a median follow-up of 9 years. In 798/918 (86.9%) patients, NMTC was sporadic, while the remaining 120 (13.1%) were familial NMTC (FNMTC).

RESULTS

We identified 119/918 (13%) patients with SMN in association with NMTC. NMTCs had an increased risk of SMN when compared to the general population (SIR 2.1, 95% CI 1.7-2.5). The rate of SMN for all sites was significantly higher in familial compared to sporadic NMTC (20% versus 11.9%, p = 0.01), primarily driven by families with more than two affected members. The risk of SMN was remarkably higher for breast cancer, especially in familial cases (SIR 22.03, 95% CI 14.4-41.2) compared to sporadic cases (SIR:17, 95% CI 11.9-24.6).

CONCLUSIONS

NMTC patients have a higher risk of SMN compared to the general population and this risk is much higher in patients with FNMTC. This observation raises the hypothesis that genetic risk factors for a first cancer may predispose to SMN, especially among individuals with familial clustering of the same or other tumors.

Side effects of theragnostic agents currently employed in clinical practice

Nuclear medicine plays an increasingly important role in several neoplasms management through a theragnostic approach by which targeted molecular imaging and radiotherapy are obtained with the use of radionuclide pairs with similar characteristics. In some cases, nuclear theragnostic use a pair of agents with identical chemical and biological characteristics while in others are employed theragnostic molecules which are not chemically or biologically identical but show similar biodistribution (so-called "twins in spirit" radiopharmaceuticals). This strategy was developed for the first time over 75 years ago, when iodine-131 was used for diagnostic imaging, confirmation of target expression and radionuclide therapy of thyroid cancer. Other theragnostic approaches were subsequently introduced with significant clinical results and some of them are currently considered standard treatment for different cancers. However, as any other therapy, also nuclear theragnostic treatment carries the potential risk of early deterministic and late stochastic off-target adverse effects, generally minimal and easily managed. This article reviews the reported side effects and risks of the main radiopharmaceuticals used for nuclear theragnostic in oncology for the treatment of thyroid cancer, neuroendocrine neoplasms, adrenergic tumors, metastatic prostate cancer, and liver tumors. Selecting appropriate patients using a multidisciplinary approach, meticulous pretreatment planning and knowledge of methods permit to decrease the incidence of these potential side effects.

Risk of primary breast cancer in patients with differentiated thyroid cancer undergoing radioactive iodine therapy: a systematic review and meta-analysis

PURPOSE

Although it has been proven that radioactive iodine (RAI) treatment is an effective and well-tolerated procedure in patients with differentiated thyroid cancer (DTC), there is still some concern regarding the risk of developing a second primary malignancy after RAI administration. We performed a systematic review and meta-analysis to investigate the risk of primary breast cancer in patients with DTC undergoing RAI therapy.

METHODS

A comprehensive literature search of the PubMed, Scopus, and Web of Science databases was conducted according to the PRISMA statement.

RESULTS

The final analysis included 14 studies accounting for a total of 200,247 patients with DTC (98,368 treated with RAI and 101,879 not treated with RAI). The relative risk of primary breast cancer in patients with DTC treated with RAI to those not treated with RAI among studies ranged from 0.45 to 2.55, the pooled relative risk was 0.83 (95% confidence interval, 0.70-0.99), and the heterogeneity was 71.5%.

CONCLUSION

The present meta-analysis indicates that patients with DTC treated with RAI do not have a higher risk of primary breast cancer compared to those not treated with RAI. These findings suggest that RAI therapy does not increase the risk of breast cancer.

Salivary and lacrimal dysfunction after radioactive iodine for differentiated thyroid cancer: American Head and Neck Society Endocrine Surgery Section and Salivary Gland Section joint multidisciplinary clinical consensus statement of otolaryngology, ophthalmology, nuclear medicine and endocrinology

BACKGROUND

Postoperative radioactive iodine (RAI) administration is widely utilized in patients with differentiated thyroid cancer. While beneficial in select patients, it is critical to recognize the potential negative sequelae of this treatment. The prevention, diagnosis, and management of the salivary and lacrimal complications of RAI exposure are addressed in this consensus statement.

METHODS

A multidisciplinary panel of experts was convened under the auspices of the American Head and Neck Society Endocrine Surgery and Salivary Gland Sections. Following a comprehensive literature review to assess the current best evidence, this group developed six relevant consensus recommendations.

RESULTS

Consensus recommendations on RAI were made in the areas of patient assessment, optimal utilization, complication prevention, and complication management.

CONCLUSION

Salivary and lacrimal complications secondary to RAI exposure are common and need to be weighed when considering its use. The recommendations included in this statement provide direction for approaches to minimize and manage these complications.

Nonthyroidal second primary malignancies in differentiated thyroid cancer patients: Is the incidence increased comparing to the general population and could it be a radioiodine therapy consequence?

The long-term survival of differentiated thyroid cancer (DTC) patients and the need to perform several treatments with radioiodine (131-I) lead to the question if the lifetime risk of developing a nonthyroidal second primary cancer (NTSPC) is increased in these patients. In our study, we assessed the prevalence of NTSPCs in thyroid cancer population and evaluated the possible causative role of 131-I treatment. We analyzed 1096 consecutive patients followed at our institution from 1964 to 1998. A total of 101 NTSPCs were observed in 92/1096 patients (8.4%) among which 17/101 (16.8%) diagnosed before DTC and 84/101 (83.2%) diagnosed after. The most frequent tumor sites observed were breast and bladder/urinary tract in the post-DTC group and breast and hematological system in the pre-DTC group. Regarding 131-I treatment, we did not observe any significant differences regarding either the number of treatments or the cumulative activity. The only significant parameter associated with an increased incidence of NTSPC was follow-up (P = .02): a longer follow-up period was associated with a higher number of NTSPCs. The mean latency between 131-I and NTSPC was 10.52 ± 7.69 years. Comparing with the general Italian population, independent of radioiodine treatment, the standard incidence ratio in our cohort was similar to that of the general population (SIR 1.07) and this result was confirmed by analyzing only the treated group. In conclusion, these results show that the risk of NTSPCs in the DTC patients' population is similar to that in the general population and 131-I treatment was not associated with an increased risk.

Breast Cancer After Treatment of Differentiated Thyroid Cancer With Radioiodine in Young Females: What We Know and How to Investigate Open Questions. Review of the Literature and Results of a Multi-Registry Survey

Published studies on the risk of radiation-induced second primary malignancy (SPM) after radioiodine treatment (RAI) of differentiated thyroid cancer (DTC) refer mainly to patients treated as middle-aged or older adults and are not easily generalizable to those treated at a younger age. Here we review available literature on the risk of breast cancer as an SPM after RAI of DTC with a focus on females undergoing such treatment in childhood, adolescence, or young adulthood. Additionally, we report the results of a preliminary international survey of patient registries from academic tertiary referral centers specializing in pediatric DTC. The survey sought to evaluate the availability of sufficient patient data for a potential international multicenter observational case-control study of females with DTC given RAI at an early age. Our literature review identified a bi-directional association of DTC and breast cancer. The general breast cancer risk in adult DTC survivors is low, ~2%, slightly higher in females than in males, but presumably lower, not higher, in those diagnosed as children or adolescents than in those diagnosed at older ages. RAI presumably does not substantially influence breast cancer risk after DTC. However, data from patients given RAI at young ages are sparse and insufficient to make definitive conclusions regarding age dependence of the risk of breast cancer as a SPM after RAI of DTC. The preliminary analysis of data from 10 thyroid cancer registries worldwide, including altogether 6,449 patients given RAI for DTC and 1,116 controls, i.e., patients not given RAI, did not show a significant increase of breast cancer incidence after RAI. However, the numbers of cases and controls were insufficient to draw statistically reliable conclusions, and the proportion of those receiving RAI at the earliest ages was too low.In conclusion, a potential international multicenter study of female patients undergoing RAI of DTC as children, adolescents, or young adults, with a sufficient sample size, is feasible. However, breast cancer screening of a larger cohort of DTC patients is not unproblematic for ethical reasons, due to the likely, at most slightly, increased risk of breast cancer post-RAI and the expected ~10% false-positivity rate which potentially produced substantial "misdiagnosis."

A Systematic Review and Meta-Analysis of Subsequent Malignant Neoplasm Risk After Radioactive Iodine Treatment of Thyroid Cancer

Background: The potential risk of subsequent malignant neoplasms (SMNs) after radioactive iodine (RAI) treatment of thyroid cancer (TC) is an important concern. Methods: A systematic review was updated comparing the risk of SMNs in TC patients treated with RAI to TC patients without RAI. Six electronic databases were searched (up to March, 2018), supplemented with a hand search. Two reviewers independently screened citations, reviewed full-text papers, and critically appraised/abstracted data. Random-effects meta-analyses were conducted using crude data and data statistically adjusted for confounders. The outcomes were any SMN and specific SMNs for which sufficient data were available. Results: In total, 3506 unique electronic search citations and 93 full-text papers were examined, including 17 studies (3 systematic reviews and 14 original studies). Published knowledge syntheses were limited by inclusion of small numbers of studies, with two systematic reviews suggesting an increased risk of any SMN and one meta-analysis suggesting a reduced risk of breast SMN after RAI treatment. In a meta-analysis of crude data, the risk ratio of any SMN in RAI-treated TC patients was 0.98 ([confidence interval (CI) 0.76-1.27]; n = 10 studies of 65,539 individuals, heterogeneity Q = 64.26, degrees of freedom [df] = 9, p < 0.001, I² = 85.99). The pooled risk ratio for any SMN, adjusted for confounders, was 1.16 ([CI 0.97-1.39]; n = 6 studies, data from at least 11,241 TC patients, Q = 10.86, df = 5, p = 0.054, I² = 53.96). In secondary analyses examining specific SMNs, although relatively rare, the risk of subsequent leukemia was increased, but the risk of multiple myeloma was reduced in RAI-treated TC patients. There was no significant increased relative risk of breast cancer, salivary cancer, or combined hematologic malignancies according to RAI treatment status. Conclusions: The body of evidence on whether ¹³¹I treatment of thyroid cancer is associated with the primary outcome of any SMN is highly heterogeneous and complex. More research examining the long-term risk of specific SMNs after ¹³¹I treatment is needed.

Factors Associated with Dose Determination of Radioactive Iodine Therapy for Differentiated Thyroid Cancer

Radioactive iodine (RAI) therapy for differentiated thyroid cancer has been successfully used for more than 70 years. However, there is still plenty of controversy surrounding the use and doses of radioiodine. There is insufficient evidence to answer the questions. Recent American Thyroid Association (ATA) guidelines seem to favor low-dose RAI, based on recent clinical trials and meta-analyses. However, long-term follow-up data remains limited, and there are additional factors we should consider that might affect the efficacy of RAI therapy. Therefore, until sufficient data are available, it is necessary to remain cautious about determining RAI doses by considering multiple patient-specific variables.

A Matter of Controversy: Is Radioiodine Therapy Favorable in Differentiated Thyroid Carcinoma?

Radioiodine therapy is a matter of controversy because different opinions exist about its use for differentiated thyroid carcinoma. The following article sheds light on the different opinions and explains why we advocate the use of radioiodine therapy in more than only high-risk patients. In comparison to other malignancies, differentiated thyroid carcinoma has a different tumor biology due to its usually slow growth pattern. Radioiodine therapy was first used about 75 y ago and provided cure at a time when prospective randomized controlled trials had yet to be developed. Large patient cohorts and usually at least a decade of clinical follow-up are needed to demonstrate a benefit from radioiodine therapy. Thus, especially in low-risk patients, many factors define an individual treatment decision, including tumor stage, extent of surgery, tumor biology, clinical and imaging data, life expectancy, and patient preferences.