Retinoic acid in patients with radioiodine non-responsive thyroid carcinoma

Use of multikinase inhibitors/lenvatinib concomitant with radioiodine for the treatment of radioiodine refractory differentiated thyroid cancer

Thyroid cancer is the most frequent endocrine tumor. However, in locally advanced or metastatic disease we have only two types of treatment at our disposal: radioactive iodine (RAI) when the disease is RAI-sensitive and multikinase inhibitors (MKIs), lenvatinib and sorafenib, when the disease becomes RAI-refractory (RR). This review revisits the published data on the potential combination of MKIs/lenvatinib with RAI in RR-differentiated thyroid cancer and evaluates some special situations where this combination may be of particular interest. The combination of MKIs/lenvatinib with RAI could, at least hypothetically, improve the efficacy seen in both treatments alone via a synergistic effect and with a lower rate of toxicity rates. Early preclinical data support this notion, while its generalized use awaits the results of ongoing clinical trials.

State of the Art in the Current Management and Future Directions of Targeted Therapy for Differentiated Thyroid Cancer

Two-thirds of differentiated thyroid cancer (DTC) patients with distant metastases would be classified as radioactive iodine-refractory (RAIR-DTC), evolving into a poor outcome. Recent advances underlying DTC molecular mechanisms have shifted the therapy focus from the standard approach to targeting specific genetic dysregulations. Lenvatinib and sorafenib are first-line, multitargeted tyrosine kinase inhibitors (TKIs) approved to treat advanced, progressive RAIR-DTC. However, other anti-angiogenic drugs, including single targeted TKIs, are currently being evaluated as alternative or salvage therapy after the failure of first-line TKIs. Combinatorial therapy of mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K) signalling cascade inhibitors has become a highly advocated strategy to improve the low efficiency of the single agent treatment. Recent studies pointed out targetable alternative pathways to overcome the resistance to MAPK and PI3K pathways’ inhibitors. Because radioiodine resistance originates in DTC loss of differentiation, redifferentiation therapies are currently being explored for efficacy. The present review will summarize the conventional management of DTC, the first-line and alternative TKIs in RAIR-DTC, and the approaches that seek to overcome the resistance to MAPK and PI3K pathways’ inhibitors. We also aim to emphasize the latest achievements in the research of redifferentiation therapy, immunotherapy, and agents targeting gene rearrangements in advanced DTC.

Molecular mechanisms of radioactive iodine refractoriness in differentiated thyroid cancer: Impaired sodium iodide symporter (NIS) expression owing to altered signaling pathway activity and intracellular localization of NIS

The advanced, metastatic differentiated thyroid cancers (DTCs) have a poor prognosis mainly owing to radioactive iodine (RAI) refractoriness caused by decreased expression of sodium iodide symporter (NIS), diminished targeting of NIS to the cell membrane, or both, thereby decreasing the efficacy of RAI therapy. Genetic aberrations (such as BRAF, RAS, and RET/PTC rearrangements) have been reported to be prominently responsible for the onset, progression, and dedifferentiation of DTCs, mainly through the activation of mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K)/AKT signaling pathways. Eventually, these alterations result in a lack of NIS and disabling of RAI uptake, leading to the development of resistance to RAI therapy. Over the past decade, promising approaches with various targets have been reported to restore NIS expression and RAI uptake in preclinical studies. In this review, we summarized comprehensive molecular mechanisms underlying the dedifferentiation in RAI-refractory DTCs and reviews strategies for restoring RAI avidity by tackling the mechanisms.

Novel therapeutic options for radioiodine-refractory thyroid cancer: redifferentiation and beyond

PURPOSE OF REVIEW

Radioiodine-refractory thyroid cancers represent the main cause of thyroid cancer-related death. At present, targeted therapies with multikinase inhibitors represent a unique therapeutic tool, though they have limited benefit on patient survival and severe drug-associated adverse events. This review summarizes current treatment strategies for radioiodine-refractory thyroid cancer and focuses on novel approaches to redifferentiate thyroid cancer cells to restore responsiveness to radioiodine administration.

RECENT FINDINGS

We summarize and discuss recent clinical trial findings and early data from real-life experiences with multikinase-inhibiting drugs. Possible alternative strategies to traditional redifferentiation are also discussed.

SUMMARY

The current review focuses primarily on the major advancements in the knowledge of the pathophysiology of iodine transport and metabolism and the genetic and epigenetic alterations occurring in thyroid neoplasia as described using preclinical models. Results of clinical studies employing new compounds to induce thyroid cancer cell redifferentiation by acting against specific molecular targets are also discussed. Finally, we describe the current scenario emerging from such findings as well as future perspectives.

Updates on the Management of Thyroid Cancer

The diagnostic modalities, stratification tools, and treatment options for patients with thyroid cancer have rapidly evolved since the development of the American Thyroid Association (ATA) guidelines in 2015. This review compiles newer concepts in diagnosis, stratification tools and treatment options for patients with differentiated thyroid cancer (DTC), medullary thyroid carcinoma (MTC) and anaplastic thyroid cancer (ATC). Newer developments apply precision medicine in thyroid cancer patients to avoid over-treatment in low risk disease and under-treatment in high risk disease. Among novel patient-tailored therapies are selective RET inhibitors that have shown efficacy in the treatment of MTC with limited systemic toxicity compared with non-specific tyrosine kinase inhibitors. The combination of BRAF and MEK inhibitors have revolutionized management of BRAF V600E mutant ATC. Several immunotherapeutic agents are being actively investigated in the treatment of all forms of thyroid cancer. In this review, we describe the recent advances in the diagnosis and management of DTC, MTC, and ATC, with an emphasis on novel treatment modalities.

Investigating the potential clinical benefit of Selumetinib in resensitising advanced iodine refractory differentiated thyroid cancer to radioiodine therapy (SEL-I-METRY): protocol for a multicentre UK single arm phase II trial

BACKGROUND

Thyroid cancer is the most common endocrine malignancy. Some advanced disease is, or becomes, resistant to radioactive iodine therapy (refractory disease); this holds poor prognosis of 10% 10-year overall survival. Whilst Sorafenib and Lenvatinib are now licenced for the treatment of progressive iodine refractory thyroid cancer, these treatments require continuing treatment and can be associated with significant toxicity. Evidence from a pilot study has demonstrated feasibility of Selumetinib to allow the reintroduction of I-131 therapy; this larger, multicentre study is required to demonstrate the broader clinical impact of this approach before progression to a confirmatory trial.

METHODS

SEL-I-METRY is a UK, single-arm, multi-centre, two-stage phase II trial. Participants with locally advanced or metastatic differentiated thyroid cancer with at least one measureable lesion and iodine refractory disease will be recruited from eight NHS Hospitals and treated with four-weeks of oral Selumetinib and assessed for sufficient I-123 uptake (defined as any uptake in a lesion with no previous uptake or 30% or greater increase in uptake). Those with sufficient uptake will be treated with I-131 and followed for clinical outcomes. Radiation absorbed doses will be predicted from I-123 SPECT/CT and verified from scans following the therapy. Sixty patients will be recruited to assess the primary objective of whether the treatment schedule leads to increased progression-free survival compared to historical control data.

DISCUSSION

The SEL-I-METRY trial will investigate the effect of Selumetinib followed by I-131 therapy on progression-free survival in radioiodine refractory patients with differentiated thyroid cancer showing increased radioiodine uptake following initial treatment with Selumetinib. In addition, information on toxicity and dosimetry will be collected. This study presents an unprecedented opportunity to investigate the role of lesional dosimetry in molecular radiotherapy, leading to greater personalisation of therapy. To date this has been a neglected area of research. The findings of this trial will be useful to healthcare professionals and patients alike to determine whether further study of this agent is warranted. It is hoped that the development of the infrastructure to deliver a multicentre trial involving molecular radiotherapy dosimetry will lead to further trials in this field.

TRIAL REGISTRATION

SEL-I-METRY is registered under ISRCTN17468602 , 02/12/2015.

Current Treatment Strategies in Metastasized Differentiated Thyroid Cancer

On successful completion of this activity one should be able to judge the prognosis of patients harboring metastasized differentiated thyroid cancer (DTC); identify suitable treatment regimens, taking into account the characteristics of the tumor and the patient's general condition; and know the basics of radioiodine treatment, tyrosine kinase treatment, and redifferentiation treatment for metastasized DTC.

Current Standards in Treatment of Radioiodine Refractory Thyroid Cancer

OPINION STATEMENT

Radioiodine refractory differentiated thyroid cancer (RAI-R DTC) is a challenging malignancy with limited prognosis and treatment options. Recently, clinical trials with targeted therapies have advanced the outlook of these patients, and inhibition of the vascular endothelial growth factor (VEGF) axis has led to the approval of small-molecule tyrosine kinase inhibitors (TKIs) for first-line treatment of radioiodine refractory disease. In addition to approved therapies (sorafenib and lenvatinib), other multi-targeted tyrosine kinase inhibitors that are commercially available have been recognized as viable treatment options for RAI-R DTC. Our preference is to initially use lenvatinib, given the dramatic progression-free survival (PFS) improvement versus placebo, with the caveat that 24 mg daily is not often tolerated and lower doses often used. In patients with BRAF V600E mutation, BRAF inhibitors are now considered for treatment, especially if patients are at high risk from antiangiogenic therapy. Research is continuing to evolve in identifying mechanisms related to radioiodine refractoriness, and trials are evaluating therapeutic molecules to overcome this resistance. Clinical care of patients with RAI-R DTC requires careful consideration of both patient and disease characteristics. Many patients with asymptomatic and indolent disease can be followed for years without treatment while others with high volume or rapidly progressive disease merit early intervention.

Radioiodine for High Risk and Radioiodine Refractory Thyroid Cancer: Current Concepts in Management

The management of early stage differentiated thyroid cancer (DTC) with low risk of recurrence has been the subject of much interest and investigation in the recent years. Locally advanced DTC and patients with a high risk of recurrent disease however needs further investigation. This short review will look at what constitutes high risk thyroid cancer, the definition of radioiodine refractory disease, the current management and areas of debate within this clinical setting.

Emerging strategies for managing differentiated thyroid cancers refractory to radioiodine

Efficient treatment of radio refractory thyroid cancer is still a major challenge. The recent identification of genetic and epigenetic alterations present in almost all differentiated tumors has revealed novel molecular targets, which can hopefully be exploited to create new treatments for these tumors. This review looks briefly at some of the innovative strategies currently being investigated for the treatment the radioiodine-resistant thyroid cancers.

[What's new in follicular thyroid cancer management in 2014?]

The American Thyroid Association has presented new guidelines for the management of thyroid cancer. These guidelines tend to appreciate more accurately the individual risk of patients, to adapt accordingly the treatment and the follow up. The initial risk stratification has been completed, especially precising the risk of N1 patients, follicular thyroid cancers, and the prognostic impact of molecular markers. Indications, doses and modalities of radioiodine (RAI) have been reevaluated, restricting its utilization in order to avoid overtreatment of low risk patients. Moreover the response to initial treatment allows to restratify the risk of the patients, and to adapt the monitoring and the thyroid hormone therapy management. The risk of suppressive thyroid hormone therapy has also to be considered. Concerning advanced thyroid cancer, prognosis is mainly depending on its RAI sensitivity. The systemic treatment of progressive, threatening refractory cancers is nowadays based on targeted therapy. However none of these treatments has demonstrated an improvement in overall survival, and side effects are frequent. Fagin et al presented promising results concerning short term treatment with selective inhibitors of the MAPK pathway, able to partially restore RAI sensitivity of refractory lesions in murine models, and recently in human patients.

Iodide- and glucose-handling gene expression regulated by sorafenib or cabozantinib in papillary thyroid cancer

CONTEXT

The aberrant silencing of iodide-handling genes accompanied by up-regulation of glucose metabolism presents a major challenge for radioiodine treatment of papillary thyroid cancer (PTC).

OBJECTIVE

This study aimed to evaluate the effect of tyrosine kinase inhibitors on iodide-handling and glucose-handling gene expression in BHP 2-7 cells harboring RET/PTC1 rearrangement.

MAIN OUTCOME MEASURES

In this in vitro study, the effects of sorafenib or cabozantinib on cell growth, cycles, and apoptosis were investigated by cell proliferation assay, cell cycle analysis, and Annexin V-FITC apoptosis assay, respectively. The effect of both agents on signal transduction pathways was evaluated using the Western blot. Quantitative real-time PCR, Western blot, immunofluorescence, and radioisotope uptake assays were used to assess iodide-handling and glucose-handling gene expression.

RESULTS

Both compounds inhibited cell proliferation in a time-dependent and dose-dependent manner and caused cell cycle arrest in the G0/G1 phase. Sorafenib blocked RET, AKT, and ERK1/2 phosphorylation, whereas cabozantinib blocked RET and AKT phosphorylation. The restoration of iodide-handling gene expression and inhibition of glucose transporter 1 and 3 expression could be induced by either drug. The robust expression of sodium/iodide symporter induced by either agent was confirmed, and (125)I uptake was correspondingly enhanced. (18)F-fluorodeoxyglucose accumulation was significantly decreased after treatment by either sorafenib or cabozantinib.

CONCLUSIONS

Sorafenib and cabozantinib had marked effects on cell proliferation, cell cycle arrest, and signal transduction pathways in PTC cells harboring RET/PTC1 rearrangement. Both agents could be potentially used to enhance the expression of iodide-handling genes and inhibit the expression of glucose transporter genes.

Retinoic acid receptors: from molecular mechanisms to cancer therapy

Retinoic acid (RA), the major bioactive metabolite of retinol or vitamin A, induces a spectrum of pleiotropic effects in cell growth and differentiation that are relevant for embryonic development and adult physiology. The RA activity is mediated primarily by members of the retinoic acid receptor (RAR) subfamily, namely RARα, RARβ and RARγ, which belong to the nuclear receptor (NR) superfamily of transcription factors. RARs form heterodimers with members of the retinoid X receptor (RXR) subfamily and act as ligand-regulated transcription factors through binding specific RA response elements (RAREs) located in target genes promoters. RARs also have non-genomic effects and activate kinase signaling pathways, which fine-tune the transcription of the RA target genes. The disruption of RA signaling pathways is thought to underlie the etiology of a number of hematological and non-hematological malignancies, including leukemias, skin cancer, head/neck cancer, lung cancer, breast cancer, ovarian cancer, prostate cancer, renal cell carcinoma, pancreatic cancer, liver cancer, glioblastoma and neuroblastoma. Of note, RA and its derivatives (retinoids) are employed as potential chemotherapeutic or chemopreventive agents because of their differentiation, anti-proliferative, pro-apoptotic, and anti-oxidant effects. In humans, retinoids reverse premalignant epithelial lesions, induce the differentiation of myeloid normal and leukemic cells, and prevent lung, liver, and breast cancer. Here, we provide an overview of the biochemical and molecular mechanisms that regulate the RA and retinoid signaling pathways. Moreover, mechanisms through which deregulation of RA signaling pathways ultimately impact on cancer are examined. Finally, the therapeutic effects of retinoids are reported.

Advanced radioiodine-refractory differentiated thyroid cancer: the sodium iodide symporter and other emerging therapeutic targets

Approximately 30% of patients with advanced, metastatic differentiated thyroid cancer have radioiodine-refractory disease, based on decreased expression of the sodium iodide symporter SLC5A5 (NIS), diminished membrane targeting of NIS, or both. Patients with radioiodine-refractory disease, therefore, are not amenable to (131)I therapy, which is the initial systemic treatment of choice for non-refractory metastatic thyroid cancer. Patients with radioiodine-refractory cancer have historically had poor outcomes, partly because these cancers often respond poorly to cytotoxic chemotherapy. In the past decade, however, considerable progress has been made in delineating the molecular pathogenesis of radioiodine-refractory thyroid cancer. As a result of the identification of key genetic and epigenetic alterations and dysregulated signalling pathways, multiple biologically targeted drugs, in particular tyrosine-kinase inhibitors, have been evaluated in clinical trials with promising results and have begun to meaningfully impact clinical practice. In this Review, we summarise the current knowledge of the molecular pathogenesis of advanced differentiated thyroid cancer and discuss findings from clinical trials of targeted drugs in patients with radioiodine-refractory disease. Additionally, we focus on the molecular basis of loss of NIS expression, function, or both in refractory disease, and discuss preclinical and clinical data on restoration of radioiodine uptake.

Long-term prognosis of differentiated thyroid cancer with lung metastasis in Korea and its prognostic factors

BACKGROUND

Distant metastasis, generally to lung and bone, is rare in differentiated thyroid carcinoma (DTC) and the prognosis is still elusive. We investigated long-term outcomes of lung metastasis in DTC patients and its prognostic factors.

METHODS

A retrospective review was performed of 4572 patients who underwent surgery for DTC from 1962 to 2009 at Seoul National University Hospital. Among them, 164 patients were identified with lung metastasis and 152 patients were enrolled in the final analysis. Poor prognosis was defined as progressive disease or death.

RESULTS

Of these 152 patients, 10- and 20-year survival rates were 85.0% and 71.0%, respectively. No evidence of disease, stable disease, progressive disease, and death was identified in 22.4%, 28.3%, 35.5%, and 13.8%, respectively, after 11 years of median follow-up (range 2-41 years). Older age at diagnosis (≥45 years), primary tumor size ≥2 cm, follicular thyroid cancer, metastasis diagnosed after initial evaluation or (131)I remnant ablation (late metastasis), multiple metastases other than lung, (131)I nonavidity, and the presence of macronodules (≥1 cm) were more frequent in poor prognoses. Cox proportional hazard ratio for progression-free survival showed that (131)I nonavidity was the only independent predictive factor for poor prognosis.

CONCLUSIONS

The prognosis of lung metastasis from DTC in Korea within this study was favorable. (131)I nonavidity, observed more frequently in late metastasis, was the only independent factor predicting poor prognosis.

AMP-activated protein kinase signaling is upregulated in papillary thyroid cancer

AMP-activated protein kinase (AMPK) is activated by the depletion in cellular energy levels and allows adaptive changes in cell metabolism and cell survival. Recently, our group described that AMPK plays an important role in the regulation of iodide and glucose uptake in thyroid cells. However, AMPK signaling pathway in human thyroid carcinomas has not been investigated so far.

OBJECTIVE

To evaluate the expression and activity of AMPK in papillary thyroid carcinomas.

METHODS

We examined total and phosphorylated AMPK (tAMPK and pAMPK) and phosphorylated acetyl-CoA-carboxylase (pACC) expressions through imunohistochemistry, using a tissue microarray block composed of 73 papillary thyroid carcinomas (PAP CA) or microcarcinomas (PAP MCA) and six adenoma (AD) samples from patients followed at the Federal University Hospital. The expression levels were compared with the non-neoplastic tissues from the same patient. Two different pathologists analyzed the samples and attributed scores of staining intensity and the proportion of stained cells. A total index was obtained by multiplying the values of intensity and the proportion of stained cells (INTxPROP).

RESULTS

tAMPK, pAMPK, and pACC showed a predominant cytoplasmic staining in papillary carcinomas, adenomas, and non-neoplastic thyroid tissues. However, the intensity and the proportion of stained cells were higher in carcinomas, so that a significant increase was found in the INTxPROP score both in PAP CA and PAP MCA, when compared with their respective controls.

CONCLUSION

Our results show unequivocally that AMPK pathway is highly activated in papillary thyroid carcinomas; however, more studies are necessary to understand the pathophysiological significance of AMPK activation in thyroid carcinogenesis.

Thyroid nodules and differentiated thyroid cancer: update on the Brazilian consensus

Thyroid nodules are frequent findings, especially when sensitive imaging methods are used. Although thyroid cancer is relatively rare, its incidence is increasing, particularly in terms of small tumors, which have an uncertain clinical relevance. Most patients with differentiated thyroid cancer exhibit satisfactory clinical outcomes when treatment is appropriate, and their mortality rate is similar to that of the overall population. However, relapse occurs in a considerable fraction of these patients, and some patients stop responding to conventional treatment and eventually die from their disease. Therefore, the challenge is how to identify the individuals who require more aggressive disease management while sparing the majority of patients from unnecessary treatments and procedures. We have updated the Brazilian Consensus that was published in 2007, emphasizing the diagnostic and therapeutic advances that the participants, representing several Brazilian university centers, consider most relevant in clinical practice. The formulation of the present guidelines was based on the participants' experience and a review of the relevant literature.

Selumetinib-enhanced radioiodine uptake in advanced thyroid cancer

BACKGROUND

Metastatic thyroid cancers that are refractory to radioiodine (iodine-131) are associated with a poor prognosis. In mouse models of thyroid cancer, selective mitogen-activated protein kinase (MAPK) pathway antagonists increase the expression of the sodium-iodide symporter and uptake of iodine. Their effects in humans are not known.

METHODS

We conducted a study to determine whether the MAPK kinase (MEK) 1 and MEK2 inhibitor selumetinib (AZD6244, ARRY-142886) could reverse refractoriness to radioiodine in patients with metastatic thyroid cancer. After stimulation with thyrotropin alfa, dosimetry with iodine-124 positron-emission tomography (PET) was performed before and 4 weeks after treatment with selumetinib (75 mg twice daily). If the second iodine-124 PET study indicated that a dose of iodine-131 of 2000 cGy or more could be delivered to the metastatic lesion or lesions, therapeutic radioiodine was administered while the patient was receiving selumetinib.

RESULTS

Of 24 patients screened for the study, 20 could be evaluated. The median age was 61 years (range, 44 to 77), and 11 patients were men. Nine patients had tumors with BRAF mutations, and 5 patients had tumors with mutations of NRAS. Selumetinib increased the uptake of iodine-124 in 12 of the 20 patients (4 of 9 patients with BRAF mutations and 5 of 5 patients with NRAS mutations). Eight of these 12 patients reached the dosimetry threshold for radioiodine therapy, including all 5 patients with NRAS mutations. Of the 8 patients treated with radioiodine, 5 had confirmed partial responses and 3 had stable disease; all patients had decreases in serum thyroglobulin levels (mean reduction, 89%). No toxic effects of grade 3 or higher attributable by the investigators to selumetinib were observed. One patient received a diagnosis of myelodysplastic syndrome more than 51 weeks after radioiodine treatment, with progression to acute leukemia.

CONCLUSIONS

Selumetinib produces clinically meaningful increases in iodine uptake and retention in a subgroup of patients with thyroid cancer that is refractory to radioiodine; the effectiveness may be greater in patients with RAS-mutant disease. (Funded by the American Thyroid Association and others; ClinicalTrials.gov number, NCT00970359.).

Radioiodine therapy in benign thyroid diseases: effects, side effects, and factors affecting therapeutic outcome

Radioiodine ((131)I) therapy of benign thyroid diseases was introduced 70 yr ago, and the patients treated since then are probably numbered in the millions. Fifty to 90% of hyperthyroid patients are cured within 1 yr after (131)I therapy. With longer follow-up, permanent hypothyroidism seems inevitable in Graves' disease, whereas this risk is much lower when treating toxic nodular goiter. The side effect causing most concern is the potential induction of ophthalmopathy in predisposed individuals. The response to (131)I therapy is to some extent related to the radiation dose. However, calculation of an exact thyroid dose is error-prone due to imprecise measurement of the (131)I biokinetics, and the importance of internal dosimetric factors, such as the thyroid follicle size, is probably underestimated. Besides these obstacles, several potential confounders interfere with the efficacy of (131)I therapy, and they may even interact mutually and counteract each other. Numerous studies have evaluated the effect of (131)I therapy, but results have been conflicting due to differences in design, sample size, patient selection, and dose calculation. It seems clear that no single factor reliably predicts the outcome from (131)I therapy. The individual radiosensitivity, still poorly defined and impossible to quantify, may be a major determinant of the outcome from (131)I therapy. Above all, the impact of (131)I therapy relies on the iodine-concentrating ability of the thyroid gland. The thyroid (131)I uptake (or retention) can be stimulated in several ways, including dietary iodine restriction and use of lithium. In particular, recombinant human thyrotropin has gained interest because this compound significantly amplifies the effect of (131)I therapy in patients with nontoxic nodular goiter.

New treatment modalities in advanced thyroid cancer

BACKGROUND

Thyroid cancer is a heterogeneous disease that is classified into differentiated thyroid carcinoma (DTC), undifferentiated/anaplastic thyroid carcinoma (ATC) and medullary thyroid carcinoma. Results of conventional treatment modalities in advanced thyroid cancer have been disappointing and therefore, new therapies are needed.

METHODS

We searched PubMed, The Cochrane Library, Medline and EMBASE databases and abstracts published in annual proceedings for new treatment modalities in advanced thyroid cancer. We also searched for ongoing trials in www.clinicaltrials.gov.

RESULTS

Six phase I, 17 phase II and 1 phase III trials with tyrosine kinase inhibitors were carried out. We found 2 pilot studies and 11 phase II trials with redifferentiation therapies, mainly in DTC. For antiproliferative approaches, three phase I and four phase II trials were found. Immunomodulatory gene therapy was tested in a pilot study in ATC patients. Two phase II trials were carried out with immunotherapy. One phase I and nine phase II trials were found with radionucleotide therapy in patients with DTC.

CONCLUSION

The developments in the treatment of advanced thyroid cancer are intriguing. Future trials should aim at combinations of targeted agents with or without other treatment modalities, and will hopefully contribute to further improvement of outcomes.

Follow-up of patients treated with retinoic acid for the control of radioiodine non-responsive advanced thyroid carcinoma

During thyroid tumor progression, cellular de-differentiation may occur and it is commonly accompanied by metastatic spread and loss of iodine uptake. Retinoic acid (RA) administration might increase iodine uptake in about 40% of patients, suggesting that RA could be a promising therapeutic option for radioiodine non-responsive thyroid carcinoma, although a prospective study with a long-term follow-up has not been reported. This was a clinical prospective study assessing the value of 13-cis-RA in patients with advanced thyroid carcinoma and its impact on major outcomes such as tumor regression and cancer-related death with a long-term follow-up of patients submitted to radioiodine (¹³¹I) therapy after RA administration. Sixteen patients with inoperable disease and no significant radioiodine uptake on post-therapy scan were selected. Patients were treated orally with 13-cis-RA at a dose of 1.0 to 1.5 mg·kg⁻¹·day⁻¹ for 5 weeks and then submitted to radioiodine therapy (150 mCi) after thyroxine withdrawal. A whole body scan was obtained 5 to 7 days after the radioactive iodine therapy. RECIST criteria were used to evaluate the response. An objective partial response rate was observed in 18.8%, a stable disease rate in 25% and a progression disease rate in 56.2%. Five patients died (62.5%) in the group classified as progression of disease. Progression-free survival rate (PFS) ranged from 72 to 12 months, with a median PFS of 26.5 months. RA may be an option for advanced de-differentiated thyroid cancer, due to the low rate of side effects.

Inhibitory effects of retinoic acid on invasiveness of human thyroid carcinoma cell lines in vitro

BACKGROUND

The prognosis of patients with metastasized thyroid carcinoma is not optimistic, necessitating the search for new treatment options.

AIM

Beneficial effects of retinoic acid (RA) have been suggested in thyroid cancer differentiation and the present study was performed to investigate the anti-metastatic potential of RA in respect of important determinants of metastatic behavior in thyroid carcinoma, focusing on the role of invasion-associated proteins.

MATERIALS AND METHODS

Differentiated thyroid carcinoma cell lines FTC- 133 and XTC.UC1, and anaplastic thyroid cancer cell lines C643 and HTH74 were studied. All cell lines were cultured with alltrans- RA (ATRA) or the solvent ethanol. Invasion and adhesion potency in vitro was studied by transwell experiment and short-term adhesion assay. The involvement of invasion-associated proteins, urokinase type plasminogen activator (uPA), uPA receptor (uPAR), matrix metalloproteinase-2 (MMP-2) and E-cadherin, were investigated by semi-quantitative RT-PCR and Western blot.

RESULTS

In vitro invasion assay revealed that ATRA treatment could reduce the invasive potency in all the thyroid cancer cell lines, with the most significant effect in anaplastic cancer cells. Short-term adhesion assay suggested that ATRA increases cancer cell adhesion to extracellular matrix (ECM) in C643, HTH74 and XTC.UC1, probably through a transcriptional and translational regulation of some attachment molecules. RT-PCR andWestern blot both revealed diminished expression of uPAR in all four carcinoma cell lines. In C643 and HTH74 cell lines, the expression of uPA was reduced and the expression of E-cadherin was increased, whereas the MMP-2 expression was not significantly down-regulated in ATRA-treated group. In ATRA-treated FTC-133 and XTC.UC1 cell lines, MMP-2 expression was decreased, but no significant changes in uPA and E-cadherin expression were observed.

CONCLUSIONS

The present study demonstrates the influence of ATRA on both important determinants of metastatic behavior ("de-adhesion" and proteolysis) in thyroid carcinoma cell lines, especially in anaplastic cancer cells. These findings may add to the explanations for beneficial effects of RA in the treatment of metastatic thyroid carcinomas.

Radioiodine treatment for malignant thyroid disease

Radioiodine treatment for thyroid disease has been given for half a decade in Sweden. The most common indication for treatment is hyperthyroidism, when iodine uptake is high. The situation in which radioiodine treatment is used in thyroid cancer is less favourable and measures therefore have to be taken to optimize the treatment. Treatment should be performed early in the course of the disease to achieve the highest possible differentiation. Before treatment the iodine and goitrogen intake should be kept low. Stimulation of the thyrocytes by thyroid-stimulating hormone (TSH) should be high. It is conventionally achieved by thyroid hormone withdrawal rendering the patient hypothyroid, or by the recently available recombinant human TSH (rhTSH) which can be recommended for ablation of the thyroid remnant after thyroidectomy and for treatment of metastases in fragile patients unable to undergo hypothyroidism. Finally, stunning--the negative effect of a prior test dose from radioactive iodine--should be avoided.

Effectiveness of retinoic acid treatment for redifferentiation of thyroid cancer in relation to recovery of radioiodine uptake

BACKGROUND

Retinoic acid (RA) treatment has been used for redifferentiation of metastatic thyroid neoplasia that have lost radioiodine (131I) uptake with heterogeneous results.

AIM

Retrospective analysis of the recovery rate of 131I uptake after RA treatment in patients from 11 Spanish hospitals.

METHODS

Twenty-seven patients (14 men, 13 women) with papillary [21], follicular [4], and oncocytic [2] thyroid cancer initially treated with total thyroidectomy plus 131I, and with 131I negative metastatic disease, were given 13-cis RA (0.66-1.5 mg/kg for 5-12 weeks) followed by a therapeutic 131I dose (3700-7400 MBq); 3 months later thyroglobulin levels and computed tomography imaging were performed.

RESULTS

In 9 out 27 cases (33%) (8 papillary, 1 follicular) optimal positive 131I scan was observed after RA treatment; in the remaining 18, 10 had a suboptimal uptake (7 papillary, 2 follicular, 1 oncocytic) and in the rest there was no 131I uptake recovery (6 papillary, 1 follicular, 1 oncocytic). In 17 positive responses to RA (either optimal or suboptimal) in which image follow-up was available, decrease or stabilization of metastatic growth was observed in 7, while tumor mass increased at short term in the remaining 10. No major side effects were detected.

CONCLUSION

Quite a high rate of 131I uptake recovery after RA treatment may be obtained in advanced differentiated thyroid cancer, but the potential modification of the natural course of the disease is uncertain. A better biological characterization of these tumors allowing the identification of potential responders to RA may improve the outcome of RA coadjuvant therapy.

Retinoic acid effects on thyroid function of female rats

AIMS

Retinoic acid is widely used in dermatological treatment and thyroid cancer management; however its possible side-effects on normal thyroid function remains unknown. We aimed to determine the effects of retinoic acid on thyroid function of adult female rats.

MAIN METHODS

Female Wistar rats were treated with all-trans-retinoic acid and 13-cis retinoic acid for 14 and 28 days. Then, rats were killed and thyroid function was evaluated.

KEY FINDINGS

Serum T4 and thyrotropin levels remained unchanged, while serum T3 increased in animals treated with all-trans-retinoic acid for 14 days. No changes were observed in hepatic or renal type 1 iodothyronine deiodinase (D1) activities, while thyroid D1 was higher in animals treated for 14 days with all-trans-retinoic acid, which could be related to the increased serum T3 levels. 13-cis retinoic acid increased thyroid iodide uptake after 28 days. These results show effects of retinoic acid treatment on these thyroid proteins: sodium/iodide symporter and deiodinase.

SIGNIFICANCE

Retinoic acid is able to interfere with normal thyroid function, increasing thyroid type 1 deiodinase activity, serum T3 levels and sodium/iodide symporter function. However, the effects are time- and retinoic acid isomer-dependent. Since serum thyrotropin levels did not change in any group, the effects observed are probably mediated by a direct retinoic acid effect on the normal thyroid.

New perspectives on the treatment of differentiated thyroid cancer

Even though differentiated thyroid carcinoma is a slow growing and usually curable disease, recurrence occurs in 20-40% and cellular dedifferentiation in up to 5% of cases. Conventional chemotherapy and radiotherapy have just a modest effect on advanced thyroid cancer. Therefore, dedifferentiated thyroid cancer represents a therapeutic dilemma and a critical area of research. Targeted therapy, a new generation of anticancer treatment, is planned to interfere with a specific molecular target, typically a protein that is believed to have a critical role in tumor growth or progression. Since many of the tumor-initiation events have already been identified in thyroid carcinogenesis, targeted therapy is a promising therapeutic tool for advanced thyroid cancer. Several new drugs are currently being tested in in vitro and in vivo studies and some of them are already being used in clinical trials, like small molecule tyrosine kinase inhibitors. In this review, we discuss the bases of targeted therapies, the principal drugs already tested and also options of redifferentiation therapy for thyroid carcinoma.

The importance of sodium/iodide symporter (NIS) for thyroid cancer management

The thyroid gland has the ability to uptake and concentrate iodide, which is a fundamental step in thyroid hormone biosynthesis. Radioiodine has been used as a diagnostic and therapeutic tool for several years. However, the studies related to the mechanisms of iodide transport were only possible after the cloning of the gene that encodes the sodium/iodide symporter (NIS). The studies about the regulation of NIS expression and the possibility of gene therapy with the aim of transferring NIS gene to cells that normally do not express the symporter have also become possible. In the majority of hypofunctioning thyroid nodules, both benign and malignant, NIS gene expression is maintained, but NIS protein is retained in the intracellular compartment. The expression of NIS in non-thyroid tumoral cells in vivo has been possible through the transfer of NIS gene under the control of tissue-specific promoters. Apart from its therapeutic use, NIS has also been used for the localization of metastases by scintigraphy or PET-scan with 124I. In conclusion, NIS gene cloning led to an important development in the field of thyroid pathophysiology, and has also been fundamental to extend the use of radioiodine for the management of non-thyroid tumors.

Rosiglitazone effect on radioiodine uptake in thyroid carcinoma patients with high thyroglobulin but negative total body scan: a correlation with the expression of peroxisome proliferator-activated receptor-gamma

BACKGROUND

Thyroid carcinoma patients with high thyroglobulin (Tg) level but negative total body scan (TBS) are difficult to treat with radioiodine (RAI). The objective of this study was to determine if treatment with rosiglitazone (RZ), a peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonist, was associated with an increase in RAI uptake in thyroid carcinoma patients with high serum Tg and negative TBSs. We also determined if there was a correspondence between the effect of RZ and the degree of staining for PPAR-gamma within thyroid cancer tissues.

METHODS

We prescribed 8 mg of RZ daily for 6 weeks in 23 patients with epithelial cell thyroid carcinoma who previously had negative posttherapeutic I-131 total body scans (post Rx TBSs) with high serum Tg concentrations. Diagnostic total body scans (Dx TBSs) before and 6 weeks after RZ treatment were compared. An ablative dose of I-131 was then given to all patients, and post Rx TBS was performed to evaluate RAI uptake. Immunohistochemical staining of PPAR-gamma expression in thyroid cancer biopsies was done to correlate this with possible effects of RZ on RAI uptake.

RESULTS

Seven patients had strong PPAR-gamma-positive staining in thyroid biopsies, nine patients had weakly positive staining, and seven patients had negative staining. Five of seven patients with strong staining had either positive post Rx TBS, or both Dx TBS and post Rx TBS. One of nine patients with weak staining had positive Dx TBS and post Rx TBS. In contrast, none of the seven patients with negative staining had positive TBS.

CONCLUSIONS

RZ can increase RAI uptake in thyroid tissue in the majority of patients with epithelial cell thyroid carcinoma whose previous posttherapeutic I-131 scans were negative provided they have high intensity and extent of PPAR-gamma expression in thyroid tissue. Few, if any, patients with weak or no PPAR-gamma expression in thyroid cancer tissue increase RAI uptake after RZ treatment.

Radioiodine therapy after pretreatment with bexarotene for metastases of differentiated thyroid carcinoma

OBJECTIVE

To evaluate the effects of pretreatment with the retinoid X receptor (RXR) agonist bexarotene on the efficacy of radioiodine therapy for metastases of differentiated thyroid carcinoma (DTC) with limited uptake of radioiodine (I-131).

DESIGN

An open prospective intervention study.

METHODS

Eight patients with metastases of DTC, with insufficient uptake of I-131 who showed increased uptake of radioiodine after previous treatment with bexarotene were treated with radioiodine (7400 MBq), preceded by 6 weeks of treatment with bexarotene 300 mg/day. Outcome parameters were serum thyroglobulin (Tg) levels and dimensions of metastases at computed tomography (CT), measured before and 6 months after therapy. Tissues of primary tumours were stained with antibodies against retinoic acid receptor (RAR) and RXR subtypes.

RESULTS

Bexarotene pretreatment induced radioiodine uptake in metastases in all eight patients, although uptake was only discernable at single photon emission computed tomography (SPECT) and had incomplete matching with the metastases visualized by CT scanning. Six months after radioiodine therapy, six patients had progressive disease (defined as a > 10% increase in serum Tg and/or a > 25% increase in tumour dimensions), whereas two patients had stable disease. No relationship was observed between retinoid receptor staining pattern at immunohistochemistry and the outcome of therapy.

CONCLUSIONS

Bexarotene therapy did not result in restoration of susceptibility to radioiodine therapy.

In vivo and microarray analysis of rexinoid-responsive anaplastic thyroid carcinoma

PURPOSE

Anaplastic thyroid carcinoma is rare, yet lethal despite aggressive therapy. Molecular targeting may be beneficial using the rexinoid LGD1069, a retinoid X receptor-selective agonist, as a novel treatment. In this report, we describe the efficacy of LGD1069 in anaplastic thyroid carcinoma in vitro and assess the in vivo treatment effects on a responsive cancer. Additionally, we explore potential mediators of the rexinoid effect on a responsive anaplastic thyroid cancer using comparative microarray analysis.

EXPERIMENTAL DESIGN

Anaplastic thyroid cancer cell lines DRO, ARO, and FRO were treated with LGD1069 in vitro. Responsive DRO xenograft tumors were treated with control chow or chow containing a low dose (30 mg/kg/d) or a high dose (100 mg/kg/d) of LGD1069. Comparative microarray analysis of DRO cells treated with LGD1069 compared with volume-equivalent control was assessed after 24 h of treatment to evaluate early gene expression changes.

RESULTS

DRO xenograft tumor growth was inhibited by LGD1069 treatment in a dose-dependent manner. Comparative microarray analysis showed that 80 genes had a significant increase in expression and 29 genes had a decrease in expression after 24 h of treatment with LGD1069. Expression of angiopoietin-like 4 (ANGPTL4) mRNA was increased 6.5-fold. A trend towards an increase in ANGPTL4 mRNA (not statistically significant) was seen in treated tumors in vivo and this correlated with decreased tumor vascularity and increased necrosis.

CONCLUSIONS

LGD1069 therapy decreases proliferation in an anaplastic thyroid cancer cell line that expresses retinoid X receptor-gamma, and this effect is confirmed with decreased tumor size in vivo in a nude mouse model. ANGPTL4 is increased in DRO in response to LGD1069 and may be a potential mediator of the effects of rexinoid treatment.

Isotretinoin as a diagnostic tool for localization of thyroid tissue in a thyroid cancer patient: a case report

The ability of thyroid cancer to incorporate radioiodine and to produce thyroglobulin (Tg) is an important tool for the diagnosis of tumor relapse. However, some patients show high serum Tg and negative whole body scan (WBS) since some specific thyroid properties may be lost during tumor progression. In these cases, a more careful diagnostic approach is necessary. Here, we report the case of a patient with undetectable serum Tg under levothyroxine (L-T4)-suppressive therapy and with a negative WBS 3 years after apparent thyroid remnant ablation. After detection of Tg mRNA in peripheral blood, the patient was re-investigated, and no suspicious lesions were detected by diagnostic WBS, neck ultrasonography, or thorax computerized tomography, except an elevation of serum Tg during hypothyroidism. Since retinoic acid (RA) is being used for the induction of radioiodine uptake by tumors expressing their receptors, we aimed to reveal the site of thyroid cancer relapse in this patient by isotretinoin administration. We demonstrate that apart from being a therapeutic option in some patients with thyroid cancer, RA can also be able to localize thyroid tissue in patients with high serum Tg and negative WBS.

Nódulos de tireóide e câncer diferenciado de tireóide: consenso brasileiro

Os nódulos tireoidianos constituem a principal manifestação clínica de uma série de doenças da tireóide com uma prevalência de aproximadamente 10% na população adulta. O maior desafio é excluir o câncer da tireóide, que ocorre em 5 a 10% dos casos. Os carcinomas diferenciados respondem por 90% dos casos de todas as neoplasias malignas da tireóide. A maioria dos pacientes com carcinoma diferenciado apresenta, geralmente, um bom prognóstico quando tratada adequadamente, com índices de mortalidade similares à população geral. No entanto, alguns indivíduos apresentam doença agressiva, desafiando o conhecimento atual e ilustrando a complexidade do manejo dessa neoplasia. No presente trabalho, reunimos 8 membros do Departamento de Tireóide da Sociedade Brasileira de Endocrinologia & Metabologia, para elaborarmos, por consenso, as diretrizes brasileiras no manejo dos nódulos tireoidianos e do câncer diferenciado da tireóide. Os membros participantes representam diferentes Centros Universitários do Brasil, refletindo diferentes abordagens diagnósticas e terapêuticas. Inicialmente, cada participante ficou responsável pela redação de determinado tema a ser enviado ao Coordenador, que, após revisão editorial e elaboração da primeira versão do manuscrito, enviou ao grupo para sugestões e aperfeiçoamentos. Quando concluído, o manuscrito foi novamente enviado e revisado por todos. A elaboração dessas diretrizes foi baseada na experiência dos participantes e revisão pertinente da literatura.

Retinoic acid inhibits angiogenesis and tumor growth of thyroid cancer cells

The anti-proliferative effect of retinoic acid (RA) has been documented for various tumors. Some 40% of patients with advanced and poorly differentiated thyroid cancer have been shown to respond to RA with increased uptake of radioiodine. It has been suggested that these effects may be caused by redifferentiation. Presently, little is known about the effects of RA on tumor angiogenesis, a prerequisite for growth and metastatic spread. The aim of the current study was to determine, whether tumor-induced angiogenesis of thyroid cancer is affected by RA. In vitro, the effect of 0.1/10 microM 13-cis RA on tumor cell number (MTT assay) and secretion of VEGF (ELISA) was analyzed in three thyroid cancer cell lines (FTC 236, C634 and XTC), as well as in endothelial cells (HUVEC) over several passages. In vivo, tumor growth, VEGF-expression and microvessel density (VSD) of RA treated thyroid cancer cells after xenotransplantation to nude mice was evaluated by morphometric analysis. In vitro, thyroid cancer cell lines responded to RA with reduced proliferation, ranging from 26 to 34% after 2 weeks of treatment and with up to 80% reduced secretion of VEGF. In vivo, tumor volumes of animals receiving RA were reduced by 33% (FTC 236), 27% (C643) and 6% (XTC), respectively. VSD of experimental tumors was diminished in the FTC 236 (25%) and the C643 cell line (15%), and almost unchanged in XTC tumors (7%). In vivo, VEGF-expression and apoptosis were not significantly affected by RA. In vitro, proliferation of HUVEC was inhibited by conditioned medium of C643 cells pretreated with RA (0.1/10 microM), as well as by administration of RA (0.1/10 microM). This study confirms thyroid tumor cell growth to be inhibited by RA. It demonstrates a decrease of in vitro VEGF accumulation and reduction of VSD in experimental undifferentiated thyroid carcinoma, suggesting that reduced angiogenesis may be an important mechanism responsible for the therapeutic effect of RA in thyroid cancer. Moreover, a direct anti-proliferative effect of RA on human endothelial cells is suggested.

Enhanced radioiodine uptake in a patient with poorly differentiated papillary thyroid cancer after treatment with rosiglitazone

The effect of pretreatment with the peroxisome proliferator-activated receptor (PPAR) agonist, rosiglitazone, on radioiodine uptake and serum thyroglobulin levels in a patient with radioiodine-resistant papillary thyroid cancer is described. Treatment with rosiglitazone resulted in enhanced radioiodine uptake in areas of presumed metastatic disease in the neck that were previously only faintly seen, and serum thyroglobulin fell from a pretreatment level of 41 ng/mL to less than 2 ng/mL.

Defective efficacy of retinoic acid treatment in patients with metastatic thyroid carcinoma

Radioiodine (I-131) therapy is of proven efficacy for differentiated thyroid carcinoma. However, its efficacy relies on specific uptake mechanisms, which may be lost during the evolution of the disease. Attempts to increase the iodine uptake of such tumors have been made using retinoic acid because it exerts redifferentiating effects on thyrocytes. This study aims to assess the capability of the retinoic acid (RA) treatment to reinforce iodine 131-irradiation efficacy for metastatic and progressive multi-irradiated thyroid cancer. In this clinical prospective study, 11 patients (mean age +/- 1 SD = 61 +/- 12 years, sex ratio M/F = 5/6) with a progressive disease despite iterative surgery and iodine irradiations were treated with 13-cis-retinoic acid (1.5 mg/kg day) over 8 weeks prior to I-131 irradiation. The redifferentiating effect of RA was evaluated by serum thyroglobulin (Tg) monitoring during RA treatment and qualitative analysis of iodine uptake on the post-therapeutic whole body scan. The clinical usefulness of RA treatment was assessed by clinical follow-up, Tg monitoring, and tumor size. No serious event that could possibly be related to the treatment was reported. The mean follow up time was 24.2 +/- 12 months (range 3-46 months). Iodine uptake was only slightly improved in two patients. Nevertheless, the clinical benefits of RA seem to be very poor. Five patients died of a metastatic disease. Five others presented new clinical evidences of a progressive disease. In conclusion, this prospective study demonstrates the absence of efficacy of I-131 irradiation combined with RA for the treatment of patients with aggressive, rapidly growing metastatic thyroid cancer. Thus, patients with highly aggressive disease, rapidly growing in a short period from 2 to 6 months, should not be considered for RA therapy.

Capecitabine therapy for refractory metastatic thyroid carcinoma: a case series

OBJECTIVE

There are few effective therapies for metastatic medullary (MTC) or radioiodine-resistant follicular thyroid carcinomas (FTC). We report a single institution's experience with capecitabine, a thymidylate synthase (TS) inhibitor, in the treatment of MTC and FTC.

DESIGN

We retrospectively analyzed five cases of metastatic thyroid carcinoma, three MTCs and two radioiodine-resistant FTCs, treated with capecitabine alone or in combination with other chemotherapeutics. Patients were selected for treatment based on low tumor TS immunohistochemical staining (< or =5%). Staining for thymidylate phosphorylase (TP) and dihydropyrimidine dehydrogenase (DPD) was also performed. Therapeutic response was assessed by imaging studies and serum tumor markers: calcitonin and carcinoembryonic antigen (MTC), and thyroglobulin (FTC).

MAIN OUTCOME

Two of three patients with MTC had stable disease or disease regression on capecitabine. One of these patients had a 90% reduction in calcitonin and stabilization by imaging that lasted 4 years. Both patients with FTC initially had stable disease on capecitabine. One patient, who was treated with capecitabine in combination first with doxorubicin and then etoposide, had an initial decrease in tumor burden, followed by stable disease for 2.8 years. The second patient had stable disease, but capecitabine was discontinued after 11 months because of hand/foot syndrome.

CONCLUSIONS

This series demonstrates promising results for the use of capecitabine in treatment of MTC and radioiodine-resistant FTC, for which there is a limited repertoire of therapeutic agents. Larger studies are needed to confirm these findings and to establish the role of fluoropyramidine metabolism markers in predicting response.

Abordagem dos pacientes com carcinoma diferenciado de tireóide com tireoglobulina sérica elevada e pesquisa de corpo inteiro negativa

No seguimento do carcinoma diferenciado de tireóide (CDT), o achado de tireoglobulina (Tg) elevada e pesquisa de corpo inteiro (PCI) diagnóstica negativa não é incomum. Em 12% dos nossos pacientes tratados com tireoidectomia e radioiodo com Tg >10ng/ml em hipotireoidismo apresentou PCI diagnóstica negativa. Este achado geralmente indica resultado falso-negativo da PCI. Devem ser excluídos exposição inadequada ao excesso de iodo e elevação insuficiente do TSH. Micrometástases que não captam o suficiente para serem detectadas com baixa atividade de radioiodo e perda da capacidade de expressar o simportador sódio/iodeto (NIS) também explicam alguns casos. Em pacientes com Tg elevada, metástases podem ser reveladas após uma dose terapêutica de radioiodo (100mCi ou mais), estando esta indicada nos casos com Tg maior que 10ng/ml em hipotireoidismo ou 5ng/ml com TSH recombinante, após exclusão de macrometástases pulmonares e cervicais. Cinco de 7 pacientes com estes critérios apresentaram captação ectópica na PCI pós-dose em nossa série. Se a PCI pós-dose for negativa ou revelar captação discreta em leito tireoidiano, outros métodos, por exemplo FDG-PET, podem ser utilizados, não se insisitindo na radioiodoterapia. Para estes casos, outras modalidades terapêuticas (cirurgia, radioterapia, quimioterapia, ácido retinóico) podem ser utilizadas. Se a PCI revelar metástases linfonodais, cirurgia é a terapia mais adequada; enquanto para metástases pulmonares difusas indica-se a radioiodoterapia até a negativação da PCI pós-dose ou normalização da Tg com TSH elevado. Pacientes com PCI pós-dose positiva podem apresentar redução significativa da Tg e até remissão completa com radioidodoterapia em alguns casos, mas o impacto deste tratamento na mortalidade permanece indefinido.