Results of rosiglitazone therapy in patients with thyroglobulin-positive and radioiodine-negative advanced differentiated thyroid cancer

Multidisciplinary Canadian consensus on the multimodal management of high-risk and radioactive iodine-refractory thyroid carcinoma

Most follicular cell-derived differentiated thyroid carcinomas are regarded as low-risk neoplasms prompting conservative therapeutic management. Here, we provide consensus recommendations reached by a multidisciplinary group of endocrinologists, medical oncologists, pathologists, radiation oncology specialists, a surgeon and a medication reimbursement specialist, addressing more challenging forms of this malignancy, focused on radioactive iodine (RAI)-resistant or -refractory differentiated thyroid carcinoma (RAIRTC). In this document we highlight clinical, radiographic, and molecular features providing the basis for these management plans. We distinguish differentiated thyroid cancers associated with more aggressive behavior from thyroid cancers manifesting as poorly differentiated and/or anaplastic carcinomas. Treatment algorithms based on risk-benefit assessments of different multimodal therapy approaches are also discussed. Given the scarcity of data supporting management of this rare yet aggressive disease entity, these consensus recommendations provide much needed guidance for multidisciplinary teams to optimally manage RAIRTC.

Diabetes Mellitus and Thyroid Cancers: Risky Correlation, Underlying Mechanisms and Clinical Prevention

The incidences of thyroid cancer and diabetes are rapidly increasing worldwide. The relationship between thyroid cancer and diabetes is a popular topic in medicine. Increasing evidence has shown that diabetes increases the risk of thyroid cancer to a certain extent. This mechanism may be related to genetic factors, abnormal thyroid-stimulating hormone secretion, oxidative stress injury, hyperinsulinemia, elevated insulin-like growth factor-1 levels, abnormal secretion of adipocytokines, and increased secretion of inflammatory factors and chemokines. This article reviews the latest research progress on the relationship between thyroid cancer and diabetes, including the association between diabetes and the risk of developing thyroid cancer, its underlying mechanisms, and potential anti-thyroid cancer effects of hypoglycemic drugs. It providing novel strategies for the prevention, treatment, and improving the prognosis of thyroid cancer.

Drug repositioning in thyroid cancer treatment: the intriguing case of anti-diabetic drugs

Cancer represents the main cause of death worldwide. Thyroid cancer (TC) shows an overall good rate of survival, however there is a percentage of patients that do not respond or are refractory to common therapies. Thus new therapeutics strategies are required. In the past decade, drug repositioning become very important in the field of cancer therapy. This approach shows several advantages including the saving of: i) time, ii) costs, iii) de novo studies regarding the safety (just characterized) of a drug. Regarding TC, few studies considered the potential repositioning of drugs. On the other hand, certain anti-diabetic drugs, were the focus of interesting studies on TC therapy, in view of the fact that they exhibited potential anti-tumor effects. Among these anti-diabetic compounds, not all were judjed as appropriate for repositioning, in view of well documented side effects. However, just to give few examples biguanides, DPP-4-inhibitors and Thiazolidinediones were found to exert strong anti-cancer effects in TC. Indeed, their effects spaced from induction of citotoxicity and inhibition of metastatic spread, to induction of de-differentiation of TC cells and modulation of TC microenvironment. Thus, the multifacial anti-cancer effect of these compounds would make the basis also for combinatory strategies. The present review is aimed at discuss data from studies regarding the anti-cancer effects of several anti-diabetic drugs recently showed in TC in view of their potential repositioning. Specific examples of anti-diabetic repositionable drugs for TC treatment will also be provided.

Radioiodine therapy in advanced differentiated thyroid cancer: Resistance and overcoming strategy

Thyroid cancer is the most prevalent endocrine tumor and its incidence is fast-growing worldwide in recent years. Differentiated thyroid cancer (DTC) is the most common pathological subtype which is typically curable with surgery and Radioactive iodine (RAI) therapy (approximately 85%). Radioactive iodine is the first-line treatment for patients with metastatic Papillary Thyroid Cancer (PTC). However, 60% of patients with aggressive metastasis DTC developed resistance to RAI treatment and had a poor overall prognosis. The molecular mechanisms of RAI resistance include gene mutation and fusion, failure to transport RAI into the DTC cells, and interference with the tumor microenvironment (TME). However, it is unclear whether the above are the main drivers of the inability of patients with DTC to benefit from iodine therapy. With the development of new biological technologies, strategies that bolster RAI function include TKI-targeted therapy, DTC cell redifferentiation, and improved drug delivery via extracellular vesicles (EVs) have emerged. Despite some promising data and early success, overall survival was not prolonged in the majority of patients, and the disease continued to progress. It is still necessary to understand the genetic landscape and signaling pathways leading to iodine resistance and enhance the effectiveness and safety of the RAI sensitization approach. This review will summarize the mechanisms of RAI resistance, predictive biomarkers of RAI resistance, and the current RAI sensitization strategies.

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.

Poorly differentiated thyroid carcinoma: a clinician's perspective

Poorly differentiated thyroid carcinoma (PDTC) is a rare thyroid carcinoma originating from follicular epithelial cells. No explicit consensus can be achieved to date due to sparse clinical data, potentially compromising the outcomes of patients. In this comprehensive review from a clinician's perspective, the epidemiology and prognosis are described, diagnosis based on manifestations, pathology, and medical imaging are discussed, and both traditional and emerging therapeutics are addressed as well. Turin consensus remains the mainstay diagnostic criteria for PDTC, and individualized assessments are decisive for treatment option. The prognosis is optimal if complete resection is performed at early stage but dismal in nearly half of patients with locally advanced and/or distant metastatic diseases, in which adjuvant therapies such as 131I therapy, external beam radiation therapy, and chemotherapy should be incorporated. Emerging therapeutics including molecular targeted therapy, differentiation therapy, and immunotherapy deserve further investigations to improve the prognosis of PDTC patients with advanced disease.

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.

Thyroid Carcinoma: Phenotypic Features, Underlying Biology and Potential Relevance for Targeting Therapy

Thyroid carcinoma consists a group of phenotypically heterogeneous cancers. Recent advances in biological technologies have been advancing the delineation of genetic, epigenetic, and non-genetic factors that contribute to the heterogeneities of these cancers. In this review article, we discuss new findings that are greatly improving the understanding of thyroid cancer biology and facilitating the identification of novel targets for therapeutic intervention. We review the phenotypic features of different subtypes of thyroid cancers and their underlying biology. We discuss recent discoveries in thyroid cancer heterogeneities and the critical mechanisms contributing to the heterogeneity with emphases on genetic and epigenetic factors, cancer stemness traits, and tumor microenvironments. We also discuss the potential relevance of the intratumor heterogeneity in understanding therapeutic resistance and how new findings in tumor biology can facilitate designing novel targeting therapies for thyroid cancer.

Advancements in the treatment of differentiated thyroid cancer

Derived from follicular epithelial cells, differentiated thyroid cancer (DTC) accounts for the majority of thyroid malignancies. The threefold increase in DTC incidence over the last three decades has been largely attributed to advancements in detection of papillary thyroid microcarcinomas. Efforts to address the issue of overtreatment have notably included the reclassification of encapsulated follicular variant papillary thyroid cancers (EFVPTC) to non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP). In the last 5 years, the overall management approach for this relatively indolent cancer has become less aggressive. Although surgery and radioiodine ablation remain the mainstay of DTC therapy, the role of active surveillance is being explored. Furthermore, the most recent American Thyroid Association (ATA) guidelines offer flexibility between lobectomy and total thyroidectomy for thyroid nodules between 1 cm and 4 cm in the absence of extrathyroidal extension or nodal disease. As our understanding of the natural history and molecular underpinnings of DTC evolves, so might our approach to managing low-risk patients, obviating the need for invasive intervention. Simultaneously, advances in interventional and systemic therapies have greatly expanded treatment options for high-risk surgical candidates and patients with widespread disease, and continue to be areas of active investigation. Continued research efforts are essential to improve our ability to offer effective individualized therapy to patients at all disease stages and to reduce the incidence of recurrent and progressive disease.

Novel Therapeutics in Radioactive Iodine-Resistant Thyroid Cancer

Iodine-resistant cancers account for the vast majority of thyroid related mortality and, until recently, there were limited therapeutic options. However, over the last decade our understanding of the molecular foundation of thyroid function and carcinogenesis has driven the development of many novel therapeutics. These include FDA approved tyrosine kinase inhibitors and small molecular inhibitors of VEGFR, BRAF, MEK, NTRK and RET, which collectively have significantly changed the prognostic outlook for this patient population. Some therapeutics can re-sensitize de-differentiated cancers to iodine, allowing for radioactive iodine treatment and improved disease control. Remarkably, there is now an FDA approved treatment for BRAF-mutated patients with anaplastic thyroid cancer, previously considered invariably and rapidly fatal. The treatment landscape for iodine-resistant thyroid cancer is changing rapidly with many new targets, therapeutics, clinical trials, and approved treatments. We provide an up-to-date review of novel therapeutic options in the treatment of iodine-resistant thyroid cancer.

Differential Effects of Estrogen Receptor Alpha and Beta on Endogenous Ligands of Peroxisome Proliferator-Activated Receptor Gamma in Papillary Thyroid Cancer

PURPOSE

The inhibition of estrogen receptor alpha (ERα) or the activation of ERβ can inhibit papillary thyroid cancer (PTC), but the precise mechanism is not known. We aimed to explore the role of ERα and ERβ on the production of endogenous peroxisome proliferator-activated receptor gamma (PPARγ) ligands in PTC.

METHODS

2 PTC cell lines, 32 pairs of PTC tissues and matched normal thyroid tissues were used in this study. The levels of endogenous PPARγ ligands 15(S)-hydroxyeicosatetraenoic acid (15(S)-HETE), 13-S-hydroxyoctadecadienoic acid (13(S)-HODE), and15-deoxy-Δ12,14-prostaglandin J2 (PGJ2) were measured by ELISA.

RESULTS

The levels of PGJ2 and 15(S)-HETE were significantly reduced in PTC, but 13(S)-HODE was not changed. Activation of ERα or inhibition of ERβ significantly downregulated the production of PGJ2, 15(S)-HETE and 13(S)-HODE, whereas inhibition of ERα or activation of ERβ markedly upregulated the production of these three ligands. Application of endogenous PPARγ ligands inhibited growth, induced apoptosis of cancer cells, and promoted the efficacy of chemotherapy.

CONCLUSION

The levels of endogenous PPARγ ligands PGJ2 and 15(S)-HETE are significantly decreased in PTC. The inhibition of ERα or activation of ERβ can inhibit PTC by stimulating the production of endogenous PPARγ ligands to induce apoptosis in cancer cells.

Exploration and Development of PPAR Modulators in Health and Disease: An Update of Clinical Evidence

Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors that govern the expression of genes responsible for energy metabolism, cellular development, and differentiation. Their crucial biological roles dictate the significance of PPAR-targeting synthetic ligands in medical research and drug discovery. Clinical implications of PPAR agonists span across a wide range of health conditions, including metabolic diseases, chronic inflammatory diseases, infections, autoimmune diseases, neurological and psychiatric disorders, and malignancies. In this review we aim to consolidate existing clinical evidence of PPAR modulators, highlighting their clinical prospects and challenges. Findings from clinical trials revealed that different agonists of the same PPAR subtype could present different safety profiles and clinical outcomes in a disease-dependent manner. Pemafibrate, due to its high selectivity, is likely to replace other PPARα agonists for dyslipidemia and cardiovascular diseases. PPARγ agonist pioglitazone showed tremendous promises in many non-metabolic disorders like chronic kidney disease, depression, inflammation, and autoimmune diseases. The clinical niche of PPARβ/δ agonists is less well-explored. Interestingly, dual- or pan-PPAR agonists, namely chiglitazar, saroglitazar, elafibranor, and lanifibranor, are gaining momentum with their optimistic outcomes in many diseases including type 2 diabetes, dyslipidemia, non-alcoholic fatty liver disease, and primary biliary cholangitis. Notably, the preclinical and clinical development for PPAR antagonists remains unacceptably deficient. We anticipate the future design of better PPAR modulators with minimal off-target effects, high selectivity, superior bioavailability, and pharmacokinetics. This will open new possibilities for PPAR ligands in medicine.

Radioactive Iodine-Refractory Differentiated Thyroid Cancer and Redifferentiation Therapy

The retained functionality of the sodium iodide symporter (NIS) expressed in differentiated thyroid cancer (DTC) cells allows the further utilization of post-surgical radioactive iodine (RAI) therapy, which is an effective treatment for reducing the risk of recurrence, and even the mortality, of DTC. Whereas, the dedifferentiation of DTC could influence the expression of functional NIS, thereby reducing the efficacy of RAI therapy in advanced DTC. Genetic alternations (such as BRAF and the rearranged during transfection [RET]/papillary thyroid cancer [PTC] rearrangement) have been widely reported to be prominently responsible for the onset, progression, and dedifferentiation of PTC, mainly through activating the mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K) signaling cascades. These genetic alternations have been suggested to associate with the reduced expression of iodide-handling genes in thyroid cancer, especially the NIS gene, disabling iodine uptake and causing resistance to RAI therapy. Recently, novel and promising approaches aiming at various targets have been attempted to restore the expression of these iodine-metabolizing genes and enhance iodine uptake through in vitro studies and studies of RAI-refractory (RAIR)-DTC patients. In this review, we discuss the regulation of NIS, known mechanisms of dedifferentiation including the MAPK and PI3K pathways, and the current status of redifferentiation therapy for RAIR-DTC patients.

Targeted Therapy in Advanced Thyroid Cancer to Resensitize Tumors to Radioactive Iodine

CONTEXT

Many differentiated thyroid cancers (DTC) dedifferentiate and become radioactive iodine (RAI)-refractory (RAIR) with worse outcomes. Targeted therapy (TTx) may downregulate MAPK signaling and sensitize tumors to RAI.

OBJECTIVE

We describe patients with RAIR DTC receiving TTx with demonstrated RAI uptake allowing for iodine-131 (I131) administration.

DESIGN

Charts of patients with metastatic, progressive, RAIR DTC in whom TTx increased RAI uptake on a diagnostic whole-body scan (WBS), were reviewed. Results of WBS, I131 administration, thyroglobulin (TG) panels, and cross-sectional studies were recorded.

SETTING

Thirteen patients [median age (range), 56 (45 to 75) years; seven men] were included; 11 (85%) had DTC, two (15%) had poorly DTC. Nine (69%) had BRAF mutations, three (23%) had RAS mutations, and one (8%) was wild type. Selective BRAF or an MEK inhibitor TTx was continued for a median (range) of 14.3 (1 to 76.4) months before diagnostic WBS.

RESULTS

Nine (69%) patients were treated with I131 [median (range) activity, 204.4 (150 to 253) mCi], after which TTx was discontinued. Median (range) follow-up was 8.3 (0 to 17.4) months after I131 therapy. All nine patients had durable disease control (three had partial response, six had stable disease). TG and TG antibody levels increased in patients who demonstrated uptake before TTx, and declined in eight of the nine patients after I131 treatment. Adverse events included pneumonitis and sialadenitis.

CONCLUSION

TTx in BRAF-/RAS-mutated RAIR DTC resensitizes tumors to iodine. Subsequent I131 administration results in meaningful responses. Patient selection, adverse events, response duration, and survival impact require additional study.

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.

The Treatment of Advanced Thyroid Cancer in the Age of Novel Targeted Therapies

Until recently, patients with advanced thyroid cancers had limited options for systemic treatment. With the introduction of tyrosine kinase inhibitors (TKIs) as a promising new class of targeted therapies for thyroid cancer, suddenly patients with advanced disease were given new options to extend survival. Guidelines worldwide have been updated to include general indications for these newer agents, but questions remain regarding which agent(s) to select, when to begin treatment, and how long therapy should continue. Additionally, the true impact of TKIs on overall survival and quality-of-life in thyroid cancer patients needs further clarification. As familiarity with approved agents and longer-term data become available, better strategies for implementation of these targeted drugs will evolve to optimize benefit for patients living with metastatic disease.

Redifferentiation of Radioiodine Refractory Differentiated Thyroid Cancer for Reapplication of I-131 Therapy

Although most differentiated thyroid cancers show excellent prognosis, treating radioiodine refractory differentiated thyroid cancer (RR-DTC) is challenging. Various therapies, including chemotherapy, radiotherapy, and targeted therapy, have been applied for RR-DTC but show limited effectiveness. Redifferentiation followed by radioiodine therapy is a promising alternative therapy for RR-DTC. Retinoic acids, histone deacetylase inhibitors, and peroxisome proliferator-activated receptor-gamma agonists are classically used as redifferentiation agents, and recent targeted molecules are also used for this purpose. Appropriate selection of redifferentiation agents for each patient, using current knowledge about genetic and biological characteristics of thyroid cancer, might increase the efficacy of redifferentiation treatment. In this review, we will discuss the mechanisms of these redifferentiation agents, results of recent clinical trials, and promising preclinical results.

Targeted therapies in thyroid cancer: an extensive review of the literature

INTRODUCTION

Patients with progressive, metastatic, RAI-refractory differentiated thyroid cancer (DTC), as well as patients with advanced medullary (MTC) and anaplastic thyroid cancer represent a cohort for which therapeutic options are limited. The recent discoveries in the molecular mechanisms implicated in TC have provided insight of the pathogenesis and progression of disease. In that respect, targeted therapies have emerged as a promising alternative for the treatment of those patients. Areas covered: Tyrosine Kinase Inhibitors (TKIs) have been studied extensively in TC: sorafenib and lenvatinib have been approved by the FDA for the treatment of metastatic, RAI-refractory DTC, while vandetanib and cabozantinib are FDA approved for use in advanced MTC. Moreover, several additional TKIs, multi-targeted or specific, are currently under investigation in TC. The current manuscript provides an extensive review of the literature regarding targeted therapies in TC including the rationale behind their use, the clinical trials and an expert opinion on their use. Literature in English appearing at PubMed was thoroughly reviewed, especially manuscripts of the last 5 years. Expert commentary: Patients with advanced, progressive, metastatic TC should be evaluated for enrollment in a clinical trial or should be placed on treatment with one of the FDA- and EMA- approved agents.

Therapeutic options in papillary thyroid carcinoma: current guidelines and future perspectives

The treatment of papillary thyroid cancer is now based on individual patient risk and response to therapies. Molecular techniques are increasingly being used to risk stratify and to guide therapeutic decisions. There have been advances in the treatment of local disease through surgery or radioiodine. Directed techniques can target metastatic disease including bisphosphonates, radiofrequency ablation or radiotherapy. Systemic therapies such as tyrosine kinase inhibitors show great promise although such treatment must be individualized. Future therapies will target treating radioiodine refractory disease.

Evolving molecularly targeted therapies for advanced-stage thyroid cancers

Increased understanding of disease-specific molecular targets of therapy has led to the regulatory approval of two drugs (vandetanib and cabozantinib) for the treatment of medullary thyroid cancer (MTC), and two agents (sorafenib and lenvatinib) for the treatment of radioactive- iodine refractory differentiated thyroid cancer (DTC) in both the USA and in the EU. The effects of these and other therapies on overall survival and quality of life among patients with thyroid cancer, however, remain to be more-clearly defined. When applied early in the disease course, intensive multimodality therapy seems to improve the survival outcomes of patients with anaplastic thyroid cancer (ATC), but salvage therapies for ATC are of uncertain benefit. Additional innovative, rationally designed therapeutic strategies are under active development both for patients with DTC and for patients with ATC, with multiple phase II and phase III randomized clinical trials currently ongoing. Continued effort is being made to identify further signalling pathways with potential therapeutic relevance in thyroid cancers, as well as to elaborate on the complex interactions between signalling pathways, with the intention of translating these discoveries into effective and personalized therapies. Herein, we summarize the progress made in molecular medicine for advanced-stage thyroid cancers of different histotypes, analyse how these developments have altered - and might further refine - patient care, and identify open questions for future research.

Internal radiation therapy: a neglected aspect of nuclear medicine in the molecular era

With increasing evidence, internal radiation therapy, also known as brachytherapy, has become a neglected aspect of nuclear medicine in the molecular era. In this paper, recent developments regarding internal radiation therapy, including developments in radioiodine-131 (¹³¹I) and thyroid, radioimmunotherapy (RIT) for non-Hodgkin lymphoma (NHL), and radiopharmaceuticals for bone metastases. Relevant differences and status of their applications in China were mentioned as well. These molecular mediated internal radiation therapies are gaining increasing importance by providing palliative and curative treatments for an increasing number of diseases and becoming one of the important parts of molecular nuclear medicine.

Obesity and Diabetes: The Increased Risk of Cancer and Cancer-Related Mortality

Obesity and type 2 diabetes are becoming increasingly prevalent worldwide, and both are associated with an increased incidence and mortality from many cancers. The metabolic abnormalities associated with type 2 diabetes develop many years before the onset of diabetes and, therefore, may be contributing to cancer risk before individuals are aware that they are at risk. Multiple factors potentially contribute to the progression of cancer in obesity and type 2 diabetes, including hyperinsulinemia and insulin-like growth factor I, hyperglycemia, dyslipidemia, adipokines and cytokines, and the gut microbiome. These metabolic changes may contribute directly or indirectly to cancer progression. Intentional weight loss may protect against cancer development, and therapies for diabetes may prove to be effective adjuvant agents in reducing cancer progression. In this review we discuss the current epidemiology, basic science, and clinical data that link obesity, diabetes, and cancer and how treating obesity and type 2 diabetes could also reduce cancer risk and improve outcomes.

Targeted therapies in advanced differentiated thyroid cancer

Differentiated thyroid cancer is the most common endocrine malignancy, and its incidence has been rising rapidly over the past 10 years. Although most patients with this disease have an excellent prognosis, a subset develops a more aggressive disease phenotype refractory to conventional therapies. Until recently, there was no effective therapy for these patients. With increasing knowledge of the molecular pathogenesis of thyroid cancer, novel targeted therapies are being developed for this group of patients. Sorafenib and lenvatinib, small-molecule multikinase inhibitors, were approved for the treatment of progressive, symptomatic, radioactive iodine refractory, advanced differentiated thyroid cancer in 2013 and 2015, respectively. This represents a major innovation in the therapy of patients with advanced thyroid cancer. However, these therapies still have many limitations and further research needs to be pursued with the ultimate goal of providing safe and effective personalized therapy for patients with advanced thyroid cancer.

Chemotherapy and chemoprevention by thiazolidinediones

Thiazolidinediones (TZDs) are synthetic ligands of Peroxisome-Proliferator-Activated Receptor gamma (PPARγ). Troglitazone, rosiglitazone, and pioglitazone have been approved for treatment of diabetes mellitus type II. All three compounds, together with the first TZD ciglitazone, also showed an antitumor effect in preclinical studies and a beneficial effect in some clinical trials. This review summarizes hypotheses on the role of PPARγ in tumors, on cellular targets of TZDs, antitumor effects of monotherapy and of TZDs in combination with other compounds, with a focus on their role in the treatment of differentiated thyroid carcinoma. The results of chemopreventive effects of TZDs are also considered. Existing data suggest that the action of TZDs is highly complex and that actions do not correlate with cellular PPARγ expression status. Effects are cell-, species-, and compound-specific and concentration-dependent. Data from human trials suggest the efficacy of TZDs as monotherapy in prostate cancer and glioma and as chemopreventive agent in colon, lung, and breast cancer. TZDs in combination with other therapies might increase antitumor effects in thyroid cancer, soft tissue sarcoma, and melanoma.

New therapies for dedifferentiated papillary thyroid cancer

The number of thyroid cancers is increasing. Standard treatment usually includes primary surgery, thyroid-stimulating hormone suppressive therapy, and ablation of the thyroid remnant with radioactive iodine (RAI). Despite the generally good prognosis of thyroid carcinoma, about 5% of patients will develop metastatic disease, which fails to respond to RAI, exhibiting a more aggressive behavior. The lack of specific, effective and well-tolerated drugs, the scarcity of data about the association of multi-targeting drugs, and the limited role of radioiodine for dedifferentiated thyroid cancer, call for further efforts in the field of new drugs development. Rearranged during transfection (RET)/papillary thyroid carcinoma gene rearrangements, BRAF (B-RAF proto-oncogene, serine/threonine kinase) gene mutations, RAS (rat sarcoma) mutations, and vascular endothelial growth factor receptor 2 angiogenesis pathways are some of the known pathways playing a crucial role in the development of thyroid cancer. Targeted novel compounds have been demonstrated to induce clinical responses and stabilization of disease. Sorafenib has been approved for differentiated thyroid cancer refractory to RAI.

Thyroid dysfunction associated with follicular cell steatosis in obese male mice and humans

Adult thyroid dysfunction is a common endocrine disorder associated with an increased risk of cardiovascular disease and mortality. A recent epidemiologic study revealed a link between obesity and increased prevalence of hypothyroidism. It is conceivable that excessive adiposity in obesity might lead to expansion of the interfollicular adipose (IFA) depot or steatosis in thyroid follicular cells (thyroid steatosis, TS). In this study, we investigated the morphological and functional changes in thyroid glands of obese humans and animal models, diet-induced obese (DIO), ob/ob, and db/db mice. Expanded IFA depot and TS were observed in obese patients. Furthermore, DIO mice showed increased expression of lipogenesis-regulation genes, such as sterol regulatory element binding protein 1 (SREBP-1), peroxisome proliferator-activated receptor γ (PPARγ), acetyl coenzyme A carboxylase (ACC), and fatty acid synthetase (FASN) in the thyroid gland. Steatosis and ultrastructural changes, including distension of the endoplasmic reticulum (ER) and mitochondrial distortion in thyroid follicular cells, were uniformly observed in DIO mice and genetically obese mouse models, ob/ob and db/db mice. Obese mice displayed a variable degree of primary thyroid hypofunction, which was not corrected by PPARγ agonist administration. We propose that systemically increased adiposity is associated with characteristic IFA depots and TS and may cause or influence the development of primary thyroid failure.

Advances in thyroid cancer treatment: latest evidence and clinical potential

Advanced thyroid carcinoma is an infrequent tumor entity with limited treatment possibilities until recently. The extraordinary improvement in the comprehension of genetic and molecular alterations involving the RAS/RAF/mitogen-activated protein kinase and phosphatidylinositide 3-kinase/Akt/mammalian target of rapamycin signaling and interacting pathways that are involved in tumor survival, proliferation, differentiation, motility and angiogenesis have been the rationale for the development of new effective targeted therapies. Data coming from phase II clinical trials have confirmed the efficacy of those targeted agents against receptors in cell membrane and cytoplasmic molecules. Moreover, four of those investigational drugs, vandetanib, cabozantinib, sorafenib and lenvatinib, have reached a phase III clinical trial with favorable results in progression-free survival and overall survival in medullary thyroid carcinoma and differentiated thyroid carcinoma. Further analysis for an optimal approach has been conducted according to mutational profile and tumor subtypes. However, consistent results are still awaited and the research for adequate prognostic and predictive biomarkers is ongoing. The following report offers a comprehensive review from the rationale to the basis of targeted agents in the treatment of thyroid carcinoma. In addition, current and future therapeutic developments by the inhibition of further molecular targets are discussed in this setting.

Differentiated thyroid cancer-personalized therapies to prevent overtreatment

The concept of individualized therapy is rapidly gaining recognition in the management of patients with differentiated thyroid cancer (DTC). This Review provides an overview of the most important elements of this paradigm shift in DTC management and discusses the implications for clinical practice. In the majority of patients with DTC who have an inherently good prognosis, the extent of surgery, the dosage of (131)I therapy and the use of levothyroxine therapy are all aspects suitable for individualization, on the basis of both the stage of disease and the response to treatment. In individuals with advanced disease, newer imaging techniques, advances in (131)I therapy and the use of targeted molecular therapies (such as multitargeted kinase inhibitors) have provided new options for the personalized care of patients, for whom until recently no effective therapies were available. Individualized therapies could reduce adverse effects, including the sometimes debilitating hypothyroidism that used to be required before initiation of (131)I treatment, and major salivary gland damage, a common and unpleasant side effect of (131)I therapy. Highly individualized interdisciplinary treatment of patients with DTC might lead to improved outcomes with reduced severity and frequency of complications and adverse effects. However, in spite of ongoing research, personalized therapies remain in their infancy.

Advanced thyroid cancers: new era of treatment

Since chemotherapy has been shown to be unsuccessful in case of advanced thyroid carcinomas, the research for new therapies is fundamental. Clinical trials of many tyrosine kinase inhibitors as well as anti-angiogenic inhibitors suggest that patients with thyroid cancer could have an advantage with new target therapy. Recently, Food and Drug Administration approved two targeted therapies, vandetanib and cabozantinib for the treatment of metastatic thyroid carcinomas with acceptable outcome. We summarized the results and the toxic effects associated with these treatments reported in clinical trials. Future trials should aim at combinations of targeted agents with or without other treatment modalities to obtain a more effective result in thyroid carcinoma treatment.

Sorafenib in the treatment of radioiodine-refractory differentiated thyroid cancer: a meta-analysis

The advent of biologically targeted agents and increased understanding of thyroid carcinogenesis have generated much interest in the development of biologically targeted therapeutic agents for thyroid cancer. Among them, sorafenib is the most commonly studied drug. The current meta-analysis was carried out to estimate the efficacy and safety of sorafenib administered in radioiodine-refractory differentiated thyroid cancer patients. An electronic search was conducted using PubMed/MEDLINE and EMBASE. Statistical analyses were carried out using either random-effects or fixed-effects models according to heterogeneity. All the statistical analyses were carried out using the Stata version 12.0 software. Seven eligible studies were identified. The final results indicated that 22% of the patients (95% CI: 15-28) achieved a partial response. Hand-foot syndrome, diarrhea, fatigue, rash, weight loss, and hypertension were the most frequently observed adverse effects (AEs) associated with sorafenib use and the incidence of these AEs (all grades) was 80% (95% CI: 68-91), 68% (95% CI: 59-77), 67% (95% CI: 57-78), 66% (95% CI: 50-82), 52%(95% CI: 33-72), and 31% (95% CI: 21-42) respectively. Sixty-two percent (95% CI: 36-89) patients required dose reductions due to toxicity of sorafenib. As far as PR and AEs are concerned, the results of this meta-analysis indicate that sorafenib has a modest effect in patients with radioiodine-refractory differentiated thyroid cancer and the high incidence of AEs associated with this agent may affect the quality of patients' lives. Though the use of sorafenib in the treatment of radioiodine-refractory differentiated thyroid cancer is considered promising by most physicians working in this field, more effective agents with less toxicity and cost are still needed.

Rosiglitazone may reduce thyroid cancer risk in patients with type 2 diabetes

BACKGROUND

Whether rosiglitazone use in patients with type 2 diabetes may affect thyroid cancer risk has not been investigated.

METHODS

The reimbursement databases of all diabetic patients under oral anti-diabetic agents or insulin from 1996 to 2009 were retrieved from the National Health Insurance of Taiwan. An entry date was set at 1 January 2006, and 887,665 patients with type 2 diabetes were followed for thyroid cancer incidence until the end of 2009 for ever-users, never-users, and subgroups of rosiglitazone exposure using tertile cut-offs for time since starting rosiglitazone, duration of therapy, and cumulative dose. Hazard ratios were estimated by Cox regression.

RESULTS

There were 103,224 ever-users and 784,441 never-users, with respective numbers of incident thyroid cancer of 84 (0.08%) and 764 (0.10%), and respective incidence of 23.12 and 28.09 per 100,000 person-years. The overall multivariable-adjusted hazard ratio was not significant. However, in dose-response analyses, the adjusted hazard ratios (95% confidence intervals) were significant for the third tertile of duration of therapy (≥ 14 months) and cumulative dose (≥ 1,800 mg) for age ≥ 50 years: 0.53 (0.31-0.89) and 0.50 (0.29-0.87), respectively.

CONCLUSIONS

This study suggests that rosiglitazone use in patients with type 2 diabetes may reduce the risk of thyroid cancer.

The cross-talk between estrogen receptor and peroxisome proliferator-activated receptor gamma in thyroid cancer

BACKGROUND

Estrogen receptor (ER) and peroxisome proliferator-activated receptor gamma (PPARγ) are associated with thyroid tumorigenesis and treatment. However, the interaction between them has not been studied.

METHODS

The impact of ER over-expression or down-expression by DNA/small interfering RNA (siRNA) transfection, ERα agonists, and the ERβ agonist diarylpropiolnitrile (DPN) on PPARγ expression/activity was examined in papillary thyroid carcinoma (PTC) and anaplastic thyroid carcinoma (ATC) cells. The effects of PPARγ modulation by rosiglitazone (RTZ), a PPARγ ligand, and of PPARγ siRNA on ER expression were determined. Cellular functions reflected by cell proliferation and migration were assayed. Apoptosis was analyzed by terminal deoxynucleotidyl transferase dUTP nick-end labeling, and apoptotic-related proteins were evaluated by Western blot analysis.

RESULTS

PPARγ protein and activity were reduced by the over-expression of either ERα or ERβ, whereas repression of ERα or ERβ increased PPARγ expression. The administration of RTZ counteracted the effects of ER and also reduced their expression, particularly in PTC cells. Moreover, knockdown of PPARγ increased ER expression and activity. Functionally, ERα activation offset the inhibitory effect of PPARγ on cellular functions, but ERβ activation aggregated it and induced apoptosis, particularly in PTC cells. Finally, the interaction between ERβ and PPARγ enhanced the expression of proapoptotic molecules, such as caspase-3 and apoptosis-inducing factor.

CONCLUSIONS

This study provides evidence supporting a cross-talk between ER and PPARγ. The reciprocal interaction between PPARγ and ERβ significantly inhibits the proliferation and migration of thyroid cancer cells, providing a new therapeutic strategy against thyroid cancer.

Clinical, safety, and economic evidence in radioactive iodine-refractory differentiated thyroid cancer: a systematic literature review

BACKGROUND

Thyroid cancer is the most common endocrine malignancy, with differentiated thyroid cancer (DTC) comprising ~93% of all thyroid cancers. While most cases of DTC are curable with the use of surgery and radioactive iodine (RAI) ablation of the remaining thyroid remnant, prognosis is dire and treatment options limited when DTC becomes RAI-refractory (RAI-R). Standard cytotoxic chemotherapy has limited efficacy, making enrollment in clinical trials of novel targeted therapies the preferred treatment approach. Thus, we conducted a comprehensive systematic review of the clinical trial scientific literature with a focus on efficacy, safety, and economics to identify all potential treatment options that have been or are currently being evaluated for the treatment of RAI-R DTC.

METHODS

Embase.com (including Medline), Medline In-Process and other nonindexed citations, the Cochrane Libraries, ClinicalTrials.gov, and relevant recent conference proceedings were searched using predefined search criteria. Important inclusion criteria included English language, randomized controlled studies or interventional single-arm studies only, and studies of drug therapies only. Search results were screened utilizing the discretion of multiple researchers, and key data were abstracted.

RESULTS

Forty-five unique trials (16 full-text, 4 conference abstracts, and 25 ClinicalTrials.gov entries) were included in the clinical review. No studies that met criteria for inclusion in the economic review were identified. Among 20 trials with results available, all were Phase II and only one was randomized. The most commonly studied drugs were tyrosine kinase inhibitors (TKIs); other drugs included celecoxib, doxorubicin with interferon alpha-2b, rosiglitazone, selumetinib (AZD6244), thalidomide, VEGF trap, and vorinostat. Overall, efficacy and safety profiles were specific to treatment regimen, with objective response rates (ORR) ranging from 0% on gefitinib, rosiglitazone, VEGF trap, and vorinostat to 50% on lenvatinib, a TKI.

CONCLUSIONS

Limited clinical research and no economic research has been conducted in RAI-R DTC. Certain treatments, notably TKIs, have shown promise in Phase II trials, and two Phase III randomized placebo-controlled trials are ongoing. New research on the economic and humanistic burden of RAI-R DTC must be paired with the clinical evidence currently in development to examine the existing burden and future promise in treating patients with RAI-R DTC.

New insight into the treatment of advanced differentiated thyroid cancer

The vast majority of patients with differentiated thyroid cancer (DTC) are treated successfully with surgery and radioactive iodine ablation, yet the treatment of advanced cases is frustrating and largely ineffective. Systemic treatment with conventional cytotoxic chemotherapy is basically ineffective in most patients with advanced DTC. However, a better understanding of the genetics and biologic basis of thyroid cancers has generated opportunities for innovative therapeutic modalities, resulting in several clinical trials. We aim to delineate the latest knowledge regarding the biologic characteristics of DTC and to describe the available data related to novel targeted therapies that have demonstrated clinical effectiveness.

New molecular targeted therapy and redifferentiation therapy for radioiodine-refractory advanced papillary thyroid carcinoma: literature review

Although the majority of papillary thyroid carcinoma could be successfully managed by complete surgical resection alone or resection followed by radioiodine ablation, a small proportion of patients may develop radioiodine-refractory progressive disease which is not amenable to surgery, local ablative treatment or other treatment modalities. The use of FDG-PET/CT scan for persistent/recurrent disease has improved the accuracy of restaging as well as cancer prognostication. Given that patients with RAI-refractory disease tend to do significantly worse than those with radioiodine-avid or non-progressive disease, an increasing number of phase I and II studies have been conducted to evaluate the efficacy of new molecular targeted drugs such as the tyrosine kinase inhibitors and redifferentiation drugs. The overall response rate of these drugs ranged between 0–53%, depending on whether the patients had been previously treated with these drugs, performance status and extent of disease. However, drug toxicity remains a major concern in administration of target therapies. Nevertheless, there are also ongoing phase III studies evaluating the efficacy of these new drugs. The aim of the review was to summarize and discuss the results of these targeted drugs and redifferentiation agents for patients with progressive, radioiodine-refractory papillary thyroid carcinoma.

Differentiated thyroid cancers: a comprehensive review of novel targeted therapies

Differentiated thyroid carcinoma (DTC) accounts for more than 90% of new thyroid cancer diagnoses, and includes papillary, follicular and Hürthle cell carcinoma. The prognosis for the vast majority of individuals diagnosed with DTC is excellent, with current treatment that includes surgery, radioactive iodine ablation and postoperative thyroid-stimulating hormone suppression. Unfortunately, the small proportion of individuals who develop radioactive iodine-resistant recurrent disease have few treatment options, and the vast majority will eventually die from their disease. Recently, several novel targets for anticancer agents have been identified and offer new hope for thyroid cancer patients diagnosed with progressive disease. In addition to targeting genes commonly altered in thyroid cancer, which include mutations in BRAF, RAS and RET, proangiogenic growth factor receptors and the sodium-iodide symporter have also been targeted. Several clinical trials evaluating tyrosine kinase and angiogenesis inhibitors for treatment of individuals diagnosed with metastatic or treatment-refractory DTC are currently underway. The objective of this review is to evaluate recent clinical trials that have studied novel targeted drugs for treatment of DTC.

Effects of rosiglitazone on radioiodine negative and progressive differentiated thyroid carcinoma as assessed by ¹²⁴I PET/CT imaging

AIM

The aim of this study was to evaluate the redifferentiative and antiproliferative effects of rosiglitazone in patients with progressive differentiated thyroid cancer (DTC) without or with negligible overall radioiodine uptake.

MATERIALS AND METHODS

A total of 9 patients with progressive DTC with either no or only negligible radioiodine accumulation were enrolled in this study. Oral rosiglitazone treatment was applied for 6 months (4 mg per day for 2 weeks followed by 8 mg per day). The compatibility of the medication was initially checked twice weekly and then weekly by laboratory tests and clinical evaluation of side effects. The assessments of alterations in the doses absorbed by the tumor and in lesion sizes over the course of rosiglitazone treatment were performed using serial ¹²⁴I positron emission tomography and computed tomography imaging. The assessment time points were before enrollment and 3 and 6 months posttreatment initiation.

RESULTS

Lesion dosimetry indicated that 5 of 9 patients had an improved lesion absorbed dose per administered activity (LDpA), yielding in radioiodine therapy treatment in 4 patients. One third of the patients (3/9) were unchanged with regard to LDpA, and 1 of 9 had deteriorated LDpA. Volumetric analyses revealed that lesion sizes were regredient in 3 of 9 patients, stable in 4 of 9, and was progressive in 1 of 9. The medication was well-tolerated, and no patient developed clinically important toxicity associated with rosiglitazone treatment. In 2 of 9 of the patients, the medication was terminated after 3 months as a precaution due to progressive heart disease in one patient and bone fracture within a known osteolytic bone lesion in another patient. It is not clear that these complications were caused by rosiglitazone.

CONCLUSION

Rosiglitazone appears to be suitable as off-label therapy in radioiodine-negative and progressive DTC that lacks therapy alternatives. In Europe, rosiglitazone was removed for label use because of reported side effects during diabetes treatment. Further investigations of other available glitazone compounds are necessary.

Pioglitazone therapy in progressive differentiated thyroid carcinoma

AIM

Rosiglitazone achieved promising results in progressive differentiated thyroid carcinoma (DTC) with redifferentiative and antiproliferative effects, but has been taken off the market. Thus we evaluated another glitazone, pioglitazone, expecting similar positive results. PATIENT, MATERIALS, METHODS: Five patients with progressive DTC and no or only negligible iodine uptake were enrolled. Oral pioglitazone treatment was applied for 6 months. The re-differentiative effect was assessed by 124I-NaI PET/CT dosimetry and the anti-proliferative effect by 18F-FDG PET/CT imaging.

RESULTS

A redifferentiative effect of pioglitazone could not be shown. Lesion dosimetry indicated that 3/5 patients had unchanged no lesion absorbed dose per administered activity (LDpA) in any tumour lesion, 2/5 patients had a deterioration of LDpA within some lesions, thus radioiodine therapy was not performed in any patient. Volumetric analysis, using RECIST criteria, revealed progressive disease in 3/5 patients and stable disease in 2/5 patients. Metabolic changes, using EORTC criteria, revealed 3/5 patients with progressive metabolic disease, 1/5 patient with stable metabolic disease and 1/5 patients with partial metabolic response. The medication was well-tolerated, and no patient developed clinically important toxicity associated with the treatment.

CONCLUSION

Pioglitazone revealed some positive effects in radioiodine negative and progressive DTC patients but it did not fulfill the expectations given by the results of rosiglitazone therapy.

Do antidiabetic medications play a specific role in differentiated thyroid cancer compared to other cancer types?

The risk for differentiated thyroid cancer, like for many other types of cancer, is increased in obese individuals and people with intermediate hyperglycaemia. The incidence of all cancers, with the exception of thyroid cancer, is also increased in type 2 diabetes mellitus patients. The review compares the prevalence of thyroid carcinoma and other cancers in obese, people with intermediate hyperglycaemia and patients with diabetes and summarizes mode of action and anti-tumourigenic effect of common antidiabetic medications. The over-expression of dipeptidyl peptidase IV in the tumours, not seen in the other cancer types, is suggested as a potential reason for the unique situation in thyroid cancer.

Thyroid cancer: emerging role for targeted therapies

The histology and clinical behavior of thyroid cancer are highly diverse. Although most are indolent tumors with a very favorable outcome with the current standard of care therapy, a small subset of tumors may be among the most lethal malignancies known to man. While surgery and radioactive iodine are the standard of care for differentiated thyroid cancers (DTC) and are effective in curing a majority of such patients, those with iodine-resistant cancers pose a great challenge for clinicians, as these patients have limited treatment options and poor prognoses. Medullary thyroid carcinoma (MTC) has no effective systemic therapy despite the genetic and signaling defects that have been well characterized for the last two decades. Anaplastic thyroid cancer (ATC) is one of the most aggressive solid tumors that remains fatal despite conventional multimodality therapy. Increased understanding of the pathogenesis of papillary thyroid carcinoma, the most common type of DTC, as well as ATC, has led to the development of targeted therapies aimed at signaling pathways and angiogenesis that are critical to the development and/or progression of such tumors. Development of tyrosine kinase inhibitors targeting known pathogenetic defects in MTC has led to testing of such agents in the clinic. Numerous clinical trials have been conducted over the last 5 years to examine the effects of these targeted molecular therapies on the outcomes of patients with iodine-refractory DTC, MTC and ATC. Conduction of such trials in the last few years represents a major breakthrough in the field of thyroid cancer. Several trials testing targeted therapies offer promise for setting new standards for the future of patients with progressive thyroid cancer. The purpose of this paper is to outline the recent advances in understanding of the pathogenesis of thyroid cancer and to summarize the results of the clinical trials with these targeted therapies.

Pioglitazone induces a proadipogenic antitumor response in mice with PAX8-PPARgamma fusion protein thyroid carcinoma

Approximately 35% of follicular thyroid carcinomas harbor a chromosomal translocation that results in expression of a paired box gene 8-peroxisome proliferator-activated receptor γ gene (PPARγ) fusion protein (PPFP). To better understand the oncogenic role of PPFP and its relationship to endogenous PPARγ, we generated a transgenic mouse model that combines Cre-dependent PPFP expression (PPFP;Cre) with homozygous deletion of floxed Pten (PtenFF;Cre), both thyroid specific. Although neither PPFP;Cre nor PtenFF;Cre mice develop thyroid tumors, the combined PPFP;PtenFF;Cre mice develop metastatic thyroid cancer, consistent with patient data that PPFP is occasionally found in benign thyroid adenomas and that PPFP carcinomas have increased phosphorylated AKT/protein kinase B. We then tested the effects of the PPARγ agonist pioglitazone in our mouse model. Pioglitazone had no effect on PtenFF;Cre mouse thyroids. However, the thyroids in pioglitazone-fed PPFP;PtenFF;Cre mice decreased 7-fold in size, and metastatic disease was prevented. Remarkably, pioglitazone caused an adipogenic response in the PPFP;PtenFF;Cre thyroids characterized by lipid accumulation and the induction of a broad array of adipocyte PPARγ target genes. These data indicate that, in the presence of pioglitazone, PPFP has PPARγ-like activity that results in trans-differentiation of thyroid carcinoma cells into adipocyte-like cells. Furthermore, the data predict that pioglitazone will be therapeutic in patients with PPFP-positive carcinomas.

Thyroid cancer: pathogenesis and targeted therapy

Therapeutic options for advanced, unresectable radioiodine-resistant thyroid cancers have historically been limited. Recent progress in understanding the pathogenesis of the various subtypes of thyroid cancer has led to increased interest in the development of targeted therapies, with potential strategies including angiogenesis inhibition, inhibition of aberrant intracellular signaling in the MAPK and PI3K/AKT/mTOR pathways, radioimmunotherapy, and redifferentiation agents. On the basis of a recent positive phase III clinical trial, the RET, vascular endothelial growth factor receptor (VEGFR), and epidermal growth factor receptor (EGFR) inhibitor vandetanib has received FDA approval as of April 2011 for use in the treatment of advanced medullary thyroid cancer. Several other recent phase II clinical trials in advanced thyroid cancer have demonstrated significant activity, and multiple other promising therapeutic strategies are in earlier phases of clinical development. The recent progress in targeted therapy is already revolutionizing management paradigms for advanced thyroid cancer, and will likely continue to dramatically expand treatment options in the coming years.

Alternative medical treatment for radioiodine-refractory thyroid cancers

Thyroid cancer is one of the most rapidly increasing cancers in many countries. Although most thyroid cancers are differentiated cancers and easily treated with radioiodine (RI), a portion of differentiated and undifferentiated cancers is refractory not only to RI therapy, but also to radiotherapy and chemotherapy. Thus, various alternative therapies have been tested in RI-refractory thyroid cancers. These alternative therapies include two major categories: redifferentiation therapy and recent molecular target therapy. Several clinical trials have investigated these therapies. They demonstrated potential effects of the therapies, although the results have been somewhat limited so far. Thus, the future strategy for undifferentiated thyroid cancers will involve individualized, lesion-specific, and combined therapy. In this review, the basic mechanism of each redifferentiation and molecular target therapy is discussed, and results of recent clinical trials using these therapeutic agents are summarized.