Radioiodine for thyroid cancer--is less more?

Analysis of NIS Plasma Membrane Interactors Discloses Key Regulation by a SRC/RAC1/PAK1/PIP5K/EZRIN Pathway with Potential Implications for Radioiodine Re-Sensitization Therapy in Thyroid Cancer

The functional expression of the sodium-iodide symporter (NIS) at the membrane of differentiated thyroid cancer (DTC) cells is the cornerstone for the use of radioiodine (RAI) therapy in these malignancies. However, NIS gene expression is frequently downregulated in malignant thyroid tissue, and 30% to 50% of metastatic DTCs become refractory to RAI treatment, which dramatically decreases patient survival. Several strategies have been attempted to increase the NIS mRNA levels in refractory DTC cells, so as to re-sensitize refractory tumors to RAI. However, there are many RAI-refractory DTCs in which the NIS mRNA and protein levels are relatively abundant but only reduced levels of iodide uptake are detected, suggesting a posttranslational failure in the delivery of NIS to the plasma membrane (PM), or an impaired residency at the PM. Because little is known about the molecules and pathways regulating NIS delivery to, and residency at, the PM of thyroid cells, we here employed an intact-cell labeling/immunoprecipitation methodology to selectively purify NIS-containing macromolecular complexes from the PM. Using mass spectrometry, we characterized and compared the composition of NIS PM complexes to that of NIS complexes isolated from whole cell (WC) lysates. Applying gene ontology analysis to the obtained MS data, we found that while both the PM-NIS and WC-NIS datasets had in common a considerable number of proteins involved in vesicle transport and protein trafficking, the NIS PM complexes were particularly enriched in proteins associated with the regulation of the actin cytoskeleton. Through a systematic validation of the detected interactions by co-immunoprecipitation and Western blot, followed by the biochemical and functional characterization of the contribution of each interactor to NIS PM residency and iodide uptake, we were able to identify a pathway by which the PM localization and function of NIS depends on its binding to SRC kinase, which leads to the recruitment and activation of the small GTPase RAC1. RAC1 signals through PAK1 and PIP5K to promote ARP2/3-mediated actin polymerization, and the recruitment and binding of the actin anchoring protein EZRIN to NIS, promoting its residency and function at the PM of normal and TC cells. Besides providing novel insights into the regulation of NIS localization and function at the PM of TC cells, our results open new venues for therapeutic intervention in TC, namely the possibility of modulating abnormal SRC signaling in refractory TC from a proliferative/invasive effect to the re-sensitization of these tumors to RAI therapy by inducing NIS retention at the PM.

Ablation rate after radioactive iodine therapy in patients with differentiated thyroid cancer at intermediate or high risk of recurrence: a systematic review and a meta-analysis

Purpose

We performed a systematic review and a meta-analysis to investigate the successful ablation rate after radioiodine (RAI) administration in patients with differentiated thyroid cancer (DTC) at intermediate-high risk of recurrence.

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 9 studies accounting for 3103 patients at intermediate-high risk of recurrence. In these patients, the successful ablation rates ranged from 51 to 94% with a 71% pooled successful ablation and were higher in intermediate (72%) than in high (52%)-risk patients. Despite the rigorous inclusion standards, a significant heterogeneity among the evaluated studies was observed. Higher administered RAI activities are associated with a lower successful ablation rate in the whole population and in the subgroup of high-risk patients. Furthermore, pooled recurrence rate in intermediate-risk patients achieving successful ablation was only 2% during the subsequent 6.4-year follow-up while the pooled recurrence rate was 14% in patients who did not achieve a successful ablation.

Conclusion

In a large sample of 3103 patients at intermediate-high risk of persistent/recurrent disease, 71% of patients achieved a successful ablation. In these intermediate-risk patients, the probability of subsequent recurrence is low and most recurrence occurred in those with already abnormal findings at the first control.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00259-021-05440-x.

Mechanisms of regulating NIS transport to the cell membrane and redifferentiation therapy in thyroid cancer

Iodine is an essential constituent of thyroid hormone. Active iodide accumulation in the thyroid is mediated by the sodium iodide symporter (NIS), comprising the first step in thyroid hormone biosynthesis, which relies on the functional expression of NIS on the cell membrane. The retention of NIS expressed in differentiated thyroid cancer (DTC) cells allows further treatment with post-operative radioactive iodine (RAI) therapy. However, compared with normal thyroid tissue, differentiated thyroid tumors usually show a decrease in the active iodide conveyance and NIS is generally retained within the cells, indicating that posttranslational protein transfer to the plasma membrane is abnormal. In recent years, through in vitro studies and studies of patients with DTC, various methods have been tested to increase the transport rate of NIS to the cell membrane and increase the absorption of iodine. An in-depth understanding of the mechanism of NIS transport to the plasma membrane could lead to improvements in RAI therapy. Therefore, in this review, we discuss the current knowledge concerning the post-translational mechanisms that regulate NIS transport to the cell membrane and the current status of redifferentiation therapy for patients with RAI-refractory (RAIR)-DTC.

Long-Term Oncological Outcome Comparison between Intermediate- and High-Dose Radioactive Iodine Ablation in Patients with Differentiated Thyroid Carcinoma: A Propensity Score Matching Study

BACKGROUND

Radioactive iodine (RAI) ablation is recommended for most patients with differentiated thyroid carcinoma (DTC) after total thyroidectomy (TT). We aimed to compare long-term outcomes between intermediate-dose (100 mCi) and high-dose (150 mCi) RAI ablation therapy in patients with DTC using propensity score matching analysis.

METHODS

This was a retrospective study of 1448 patients with DTC who underwent RAI ablation after TT. Propensity score matching was performed using the extent of operation, tumor size, extrathyroidal extension, multifocality, lymphatic invasion, vascular invasion, perineural invasion, number of positive lymph nodes (LNs), ATA risk stratification system, T stage, N stage, TNM stage, preoperative serum Tg and TgAb levels, and post-RAI serum Tg and TgAb levels.

RESULTS

Recurrence rates in the intermediate- and high-dose groups were 3.1% and 5.6%, respectively. After propensity score matching, LN ratio >0.22 (HR, 2.915; 95% CI, 1.228-6.918; p=0.015) and serum Tg >10 ng/mL after RAI (HR, 3.976; 95% CI, 1.839-8.595; p < 0.001) were significant predictors of recurrence. Kaplan-Meier analysis showed no significant difference in DFS before or after propensity score matching (p=0.074 and p=0.378, respectively).

CONCLUSIONS

Intermediate-dose RAI ablation for the adjuvant treatment of DTC is sufficient as compared to high-dose RAI ablation. Further prospective or multicenter studies should be conducted to clarify the prognosis of intermediate-dose RAI ablation.

A rapidly increasing trend of thyroid cancer incidence in selected East Asian countries: Joinpoint regression and age-period-cohort analyses

BACKGROUND

This study described the incidence and mortality trends and analyzed age-period-cohort effects on incidences in China, Japan, and Korea.

METHODS

Data were extracted from the Cancer Incidence in Five Continents series and the World Health Organization Cancer Mortality Database, and the age-standardized incidence and mortality rates by Segi's world population were calculated. Joinpoint regression analysis was used to evaluate the time trend of age-standardized incidence and mortality rates and the age-period-cohort model with intrinsic estimator was applied for estimating the effects of age, period, and cohort on thyroid cancer (TC) incidence in individuals between 20 and 84 years of age.

RESULTS

An increasing trend in TC incidence rates was observed among males from China (10.3%), Japan (4.7%), and Korea (20.8%) and among females from China (9.4%), Japan (3.5%), and Korea (20.5%). TC incidence rates in females were much higher than those in males. A downward trend of TC mortality rates was observed, especially in both sexes of Japan and Chinese females. The slope of the age effect curve peaked at an earlier age in females than males in Japan and Korea. A strong period effect and remarkedly increasing rate ratios were observed in all regions and for both sexes. The cohort effect had a declining tendency on TC incidence in males and females in these areas.

CONCLUSIONS

The rapidly upward incidence trend and strong period effect suggest that overdiagnosis caused by higher diagnostic intensity might be an explanation for the upward trend, and some environmental risk factor exposures are also not excluded. In addition, the discrepant trends of TC incidence and mortality reveal the need to identify the few high-risk patients who needed further treatment from those patients who may not need treatment.

Concordance in postsurgical radioactive iodine therapy recommendations between Watson for Oncology and clinical practice in patients with differentiated thyroid carcinoma

BACKGROUND

To the authors' knowledge, the indications for radioactive iodine (RAI) therapy in patients with differentiated thyroid carcinoma (DTC) are unclear; treatment decisions are based on physician judgment. The objective of the current study was to identify the degree of concordance between postsurgical RAI therapy recommended by Watson for Oncology (WFO), a clinical decision support system for oncological therapy, and that recommended by physicians for patients with DTC.

METHODS

The current retrospective cohort study included 207 patients with DTC who underwent thyroidectomy between 2017 and 2018. Treatment recommendations were considered concordant if WFO rendered recommendations consistent with those of the physicians.

RESULTS

Treatment recommendations were concordant for 160 patients (77%). The concordance rate significantly differed according to the American Thyroid Association (ATA) risk category (P < .001) and American Joint Committee on Cancer TNM stage (seventh edition; P = .004). Logistic regression analysis demonstrated that treatment recommendations were significantly less likely to be concordant in patients with ATA intermediate-risk and stage III disease compared with those with ATA low-risk and stage I disease (odds ratio, 0.16 [P < .001] and OR, 0.35 [P = .004], respectively).

CONCLUSIONS

The authors believe the concordance rate between postsurgical RAI therapy recommendations rendered by WFO and those rendered by physicians was too low to justify adopting WFO for the comprehensive screening of patients with DTC. This is particularly true among patients with ATA intermediate-risk and stage III disease, reflecting differences in practice patterns between the United States (where WFO was calibrated) and Korea. Hence, WFO is not a substitute for physicians, and also may require regional customization to improve its assistive capability.

Implications of Na+/I- Symporter Transport to the Plasma Membrane for Thyroid Hormonogenesis and Radioiodide Therapy

Iodine is a crucial component of thyroid hormones; therefore, a key requirement for thyroid hormone biosynthesis is that iodide (I⁻) be actively accumulated in the thyroid follicular cell. The ability of the thyroid epithelia to concentrate I⁻ is ultimately dependent on functional Na⁺/ I⁻ symporter (NIS) expression at the plasma membrane. Underscoring the significance of NIS for thyroid physiology, loss-of-function mutations in the NIS-coding SLC5A5 gene cause an I⁻ transport defect, resulting in dyshormonogenic congenital hypothyroidism. Moreover, I⁻ accumulation in the thyroid cell constitutes the cornerstone for radioiodide ablation therapy for differentiated thyroid carcinoma. However, differentiated thyroid tumors often exhibit reduced (or even undetectable) I⁻ transport compared with normal thyroid tissue, and they are diagnosed as cold nodules on thyroid scintigraphy. Paradoxically, immunohistochemistry analysis revealed that cold thyroid nodules do not express NIS or express normal, or even higher NIS levels compared with adjacent normal tissue, but NIS is frequently intracellularly retained, suggesting the presence of posttranslational abnormalities in the transport of the protein to the plasma membrane. Ultimately, a thorough comprehension of the mechanisms that regulate NIS transport to the plasma membrane would have multiple implications for radioiodide therapy, opening the possibility to identify new molecular targets to treat radioiodide-refractory thyroid tumors. Therefore, in this review, we discuss the current knowledge regarding posttranslational mechanisms that regulate NIS transport to the plasma membrane under physiological and pathological conditions affecting the thyroid follicular cell, a topic of great interest in the thyroid cancer field.

Outcome after ablation in patients with low-risk thyroid cancer (ESTIMABL1): 5-year follow-up results of a randomised, phase 3, equivalence trial

BACKGROUND

In ESTIMABL1, a randomised phase 3 trial of radioactive iodine (131I) administration after complete surgical resection in patients with low-risk thyroid cancer, 92% of patients had complete thyroid ablation at 6-10 months, defined as a recombinant human thyroid-stimulating hormone (rhTSH)-stimulated serum thyroglobulin concentration of 1 ng/mL or less and normal findings on neck ultrasonography. Equivalence was shown between low-activity (1·1 GBq) and high-activity (3·7 GBq) radioactive iodine and also between the use of rhTSH injections and thyroid hormone withdrawal. Here, we report outcomes after 5 years of follow-up.

METHODS

This multicentre, randomised, open-label, equivalence trial was done at 24 centres in France. Between March 28, 2007, and Feb 25, 2010, we randomly assigned (1:1:1:1) adults with low-risk differentiated thyroid carcinoma who had undergone total thyroidectomy to one of four strategies, each combining one of two methods of thyrotropin stimulation (rhTSH or thyroid hormone withdrawal) and one of two radioactive iodine activities (1·1 GBq or 3·7 GBq). Randomisation was by computer-generated sequence, with variable block size. Follow-up consisted of a yearly serum thyroglobulin measurement on levothyroxine treatment. Measurement of rhTSH-stimulated thyroglobulin and neck ultrasonography were done at the discretion of the treating physician. No evidence of disease was defined as serum thyroglobulin of 1 ng/mL or less on levothyroxine treatment and normal results on neck ultrasonography, when performed. This study was registered with ClinicalTrials.gov, number NCT00435851.

FINDINGS

726 patients (97% of the 752 patients originally randomised) were followed up. At a median follow-up since randomisation of 5·4 years (range 0·5-9·2), 715 (98%) had no evidence of disease. The other 11 had either structural disease (n=4), raised serum thyroglobulin concentration (n=5), or indeterminate findings on neck ultrasonography (n=2). At ablation, six of these patients had received 1·1 GBq radioactive iodine (five after rhTSH and one after withdrawal) and five had received 3·7 GBq (two after rhTSH and three after withdrawal). TSH-stimulated (either after rhTSH injections or thyroid hormone withdrawal according to the treatment group) thyroglobulin concentration measured at the time of ablation was prognostic for structural disease status at ablation, ablation status at 6-10 months, and the final outcome.

INTERPRETATION

Our findings suggest that disease recurrence was not related to the strategy used for ablation. These data validate the use of 1·1 GBq radioactive iodine after rhTSH for postoperative ablation in patients with low-risk thyroid cancer.

FUNDING

French National Cancer Institute (INCa), French Ministry of Health, and Sanofi Genzyme.

Use of evidence-based guidelines reduces radioactive iodine treatment in patients with low-risk differentiated thyroid cancer

OBJECTIVE

The goal was to determine if there was a relation between the introduction of evidence-based radioactive iodine (RAI) treatment guidelines for differentiated thyroid cancer (DTC) at Cedars-Sinai Medical Center (CSMC) and subsequent RAI use. In addition, we compared RAI treatment rates for DTC at CSMC to data from the National Cancer Database (NCDB) to see if the trends in RAI use at CSMC differed from the national trends.

METHODS

RAI data from the CSMC Thyroid Cancer Center were reviewed to determine if RAI treatment was given appropriately. Kaplan-Meier curves were used to estimate disease-free survival for patients who received or did not receive treatment. RAI data from the NCDB were also used to compare how CSMC treatment rates compare nationally.

RESULTS

There were 444 CSMC patients identified with DTC between 2009 and 2012. Approximately 95% of the patients had papillary thyroid cancer (n=423) with 65% in the stage I risk group (n=290). Kaplan-Meier curves for stages I-III show that those who did not receive RAI treatment had 100% disease-free survival, which was better than those who had received RAI. However, given that the total population in both stages II and III is quite small, having received RAI ablation was not found to be statistically significant. Stage I patients who received RAI had a significantly increased incidence of recurrent disease. The NCDB RAI rates for all DTC stages in each year have consistently been over 50% with an overall treatment rate of 57%. There were significant differences in the treatment rates between CSMC and NCDB, with a decrease in the use of RAI in low-risk patients with stage I tumors at CSMC following institution of the guidelines.

CONCLUSION

Prudent use of RAI treatment should be considered for low-risk patients. Ablation rates have been decreasing steadily at CSMC, particularly among low-risk patients, with the adoption of more stringent RAI treatment guidelines. It is apparent from our data that physician practices can change with the implementation and dissemination of evidence-based guidelines for the treatment of DTC with RAI.

The AEC/NRC 30 mCi rule: regulatory origins and clinical consequences for 131I remnant ablative doses

BACKGROUND

Clinical and historical uncertainty exists surrounding the regulations of the Atomic Energy Commission/Nuclear Regulatory Commission (AEC/NRC) requiring patient hospitalization when (131)I activities exceed 30 mCi. This review investigates the sometimes disturbing regulatory and clinical origins and consequences of the use of this low, 30 mCi dose as a prescription for thyroid remnant ablation.

SUMMARY

As early as in the 1940s, activities of (131)I between 30 and 200 mCi, often fractionated, were employed. The AEC deliberated from 1947 to the early 1960s before imposing as a license condition the requirement of hospitalizing patients until they contained <30 mCi of any byproduct material. The written AEC record throughout these years contains no supportive data to suggest safety issues requiring hospitalization at this activity level of (131)I. Yet the techniques for making the necessary calculations for determining radiation safety were available at this time. Declarations on the subject by nongovernmental bodies were misinterpreted as confirming such hospitalization as a legal requirement. The 30 mCi license condition was codified into NRC regulations in 1987 and was subsequently removed in 1997. Without any data, these U.S. regulatory agencies caused significant expense, inconvenience, and fear, affecting thyroid cancer patients and their families. This 30 mCi regulatory activity limit morphed, by a fortunate coincidence, into an acceptable ablative activity before there were solid confirmatory data. Studies on this 30 mCi ablative dose indicate that this activity was never associated with radiation health and safety issues, and was never more effective than higher ablative doses but led slightly more often to the need for a second (131)I dose. Nevertheless, the available data generally support the American Thyroid Association and Society of Nuclear Medicine and Molecular Imaging Guidelines, which indicate, without a treatment activity preference, that 30-100 mCi of (131)I provide adequate ablation. Follow-up data on the rates of recurrences, deaths, and second primary malignancies within this range of doses are unavailable.

CONCLUSIONS

This history of unjustified governmental action and blind acceptance must remind the medical/radiation safety community to require solid data before ever again adopting baseless requirements. The 30 mCi dose should have never been employed as a requirement for hospitalization.

High versus low radioiodine activity in patients with differentiated thyroid cancer: a meta-analysis

BACKGROUND

The purpose of the meta-analysis was to estimate the effectiveness and toxicity of low activity radioiodine ablation versus high activity in patients with differentiated thyroid cancer (DTC).

DESIGN

A systematic review and meta-analysis was performed by including all randomized trials of low activity versus high activity radioiodine ablation after thyroidectomy. Standard meta-analytic procedures were used to analyze the study outcomes.

RESULTS

Ten trials were considered eligible and were further analyzed. The pooled risk ratio (RR) of having a successful ablation for an activity of 1100 MBq versus 3700 MBq (seven trials, 1772 patients) was 0.94 (95% CI 0.85-1.04, p-value = 0.21). The RR for successful ablation when only thyroid hormone withdrawal was used (five trials, 1116 patients) was 0.87 (95% CI 0.72-1.06, p-value = 0.17) and it was comparable to RR when only recombinant-human TSH (rec-hTSH) (two trials, 812 patients) was used (1.00, 95% CI 0.93-1.07, p-value = 0.92). Salivary dysfunction, nausea, and neck pain were significantly more frequent among patients with higher dose for ablation.

CONCLUSION

Our meta-analysis provides some evidence from randomized trials that a lower activity of radioiodine ablation is as effective as higher dose after surgery in patients with DTC with lower toxicity.

Worldwide increasing incidence of thyroid cancer: update on epidemiology and risk factors

Background. In the last decades, thyroid cancer incidence has continuously and sharply increased all over the world. This review analyzes the possible reasons of this increase. Summary. Many experts believe that the increased incidence of thyroid cancer is apparent, because of the increased detection of small cancers in the preclinical stage. However, a true increase is also possible, as suggested by the observation that large tumors have also increased and gender differences and birth cohort effects are present. Moreover, thyroid cancer mortality, in spite of earlier diagnosis and better treatment, has not decreased but is rather increasing. Therefore, some environmental carcinogens in the industrialized lifestyle may have specifically affected the thyroid. Among potential carcinogens, the increased exposure to medical radiations is the most likely risk factor. Other factors specific for the thyroid like increased iodine intake and increased prevalence of chronic autoimmune thyroiditis cannot be excluded, while other factors like the increasing prevalence of obesity are not specific for the thyroid. Conclusions. The increased incidence of thyroid cancer is most likely due to a combination of an apparent increase due to more sensitive diagnostic procedures and of a true increase, a possible consequence of increased population exposure to radiation and to other still unrecognized carcinogens.

To treat or not to treat: the role of adjuvant radioiodine therapy in thyroid cancer patients

Radioactive iodine (RAI) is used in treatment of patients with differentiated papillary and follicular thyroid cancer. It is typically used after thyroidectomy, both as a means of imaging to detect residual thyroid tissue or metastatic disease, as well as a means of treatment by ablation if such tissue is found. In this paper, we discuss the indications for and the mechanisms of RAI in the treatment of patients with thyroid cancer. We discuss the attendant risks and benefits that come with its use, as well as techniques used to optimize its effectiveness as an imaging tool and a therapeutic modality.