[Medullary thyroid carcinoma in children]

Medullary thyroid carcinoma (MTC) is rare in children. MTC is almost always inherited and occurs as part of a multiple endocrine neoplasia type 2A and B, due to germline mutation in the RET proto-oncogene. MTC in the pediatric population is most often diagnosed in the course of a familial genetic investigation. But when the child is the proband, a de novo mutation is most often founded. The main aim is to treat MTC before extrathyroidal extension occurs because when distant metastases are present, it is rarely curable. Treatment is based on total thyroidectomy with cervical lymph node dissection.

Clinical development of VEGF signaling pathway inhibitors in childhood solid tumors

Angiogenesis is a target shared by both adult epithelial cancers and the mesenchymal or embryonal tumors of childhood. Development of antiangiogenic agents for the pediatric population has been complicated by largely theoretical concern for toxicities specific to the growing child and prioritization among the many antiangiogenic agents being developed for adults. This review summarizes the mechanism of action and preclinical data relevant to childhood cancers and early-phase clinical trials in childhood solid tumors. Single-agent adverse event profiles in adults and children are reviewed with emphasis on cardiovascular, bone health, and endocrine side effects. In addition, pharmacological factors that may be relevant for prioritizing clinical trials of these agents in children are reviewed. Considerations for further clinical evaluation should include preclinical data, relative potency, efficacy in adults, and the current U.S. Food and Drug Administration approval status. Toxicity profiles of vascular endothelial growth factor (VEGF) signaling pathway inhibitors may be age dependent and ultimately, their utility in the treatment of childhood cancer will require combination with standard cytotoxic drugs or other molecularly targeted agents. In combination studies, toxicity profiles, potential drug interactions, and late effects must be considered. Studies to assess the long-term impact of VEGF signaling pathway inhibitors on cardiovascular, endocrine, and bone health in children with cancer are imperative if these agents are to be administered to growing children and adolescents with newly diagnosed cancers.

Management of medullary thyroid carcinoma and MEN2 syndromes in childhood

Medullary thyroid carcinoma (MTC) and the multiple endocrine neoplasia (MEN) type 2 syndromes are rare but important endocrine diseases that are increasingly managed by pediatric providers. MTC is generally associated with a favorable prognosis when diagnosed during childhood, where it frequently occurs secondary to activating mutations in the RET proto-oncogene and arises from pre-existing C-cell hyperplasia. MEN2A accounts for 90-95% of childhood MTC cases and is most commonly due to mutations in codon 634 of RET. MEN2B is associated with the most aggressive clinical presentation of MTC and is almost always due to the Met918Thr mutation of RET. Surgery is the primary treatment and only chance of cure, although the advent of targeted therapies seems to be improving progression-free survival in advanced cases. Since the discovery of the role of RET in MEN2A, considerable advances in the management of this syndrome have occurred, and most of the children with MEN2A who have undergone early thyroidectomy will now lead full, productive lives. Strong genotype-phenotype correlations have facilitated the development of guidelines for interventions. Contemporary approaches for deciding the appropriate age at which surgery should take place incorporate data from ultrasonography and calcitonin measurements in addition to the results of genotyping. To optimize care and to facilitate ongoing research, children with MTC and the MEN2 syndromes are optimally treated at tertiary centers with multidisciplinary expertise.

Targeted therapies for thyroid tumors

Systemic chemotherapies for advanced or metastatic thyroid carcinomas have been of only limited effectiveness. For patients with differentiated or medullary carcinomas unresponsive to conventional treatments, novel therapies are needed to improve disease outcomes. Multiple novel therapies primarily targeting angiogenesis have entered clinical trials for metastatic thyroid carcinoma. Partial response rates up to 30% have been reported in single-agent studies, but prolonged disease stabilization is more commonly observed. The most successful agents target the vascular endothelial growth factor receptors, with potential targets including the mutant kinases associated with papillary and medullary oncogenesis. Two drugs approved for other malignancies, sorafenib and sunitinib, have had promising preliminary results reported, and are being used selectively for patients who do not qualify for clinical trials. At least one randomized, placebo-controlled phase III trial has been successfully completed, showing improved progression-free survival in patients with advanced or metastatic medullary thyroid carcinoma treated with vandetanib. Randomized trials for other agents are currently underway. Treatment for patients with metastatic or advanced thyroid carcinoma now emphasizes clinical trial opportunities for novel agents with considerable promise. Alternative options now exist for use of tyrosine kinase inhibitors that are well tolerated and may prove worthy of regulatory approval for this disease.

The evolving field of tyrosine kinase inhibitors in the treatment of endocrine tumors

Activation of tyrosine kinase receptors (TKRs) and their related pathways has been associated with development of endocrine tumors. Compounds that target and inactivate the kinase function of these receptors, tyrosine kinase inhibitors (TKIs), are now being applied to the treatment of endocrine tumors. Recent clinical trials of TKIs in patients with advanced thyroid cancer, islet cell carcinoma, and carcinoid have shown promising preliminary results. Significant reductions in tumor size have been described in medullary and papillary thyroid carcinoma, although no complete responses have been reported. Case reports have described significant tumor volume reductions of malignant pheochromocytomas and paragangliomas. In addition, these compounds showed an initial tumoricidal or apoptotic response followed by long-term static effects on tumor growth. Despite the promising preliminary results, this class of therapeutic agents has a broad spectrum of adverse effects, mediated by inhibition of kinase activities in normal tissues. These adverse effects will have to be balanced with their benefit in clinical use. New strategies will have to be applied in clinical research to achieve optimal benefits. In this review, we will address the genetic alterations of TKRs, the rationale for utilizing TKIs for endocrine tumors, and current information on tumor and patient responses to specific TKIs. We will also discuss the adverse effects related to TKI treatment and the mechanisms involved. Finally, we will summarize the challenges associated with use of this class of compounds and potential solutions.

Targeted therapy of thyroid cancer

Systemic chemotherapies for advanced or metastatic thyroid carcinomas have been of only limited effectiveness. For patients with differentiated or medullary carcinomas unresponsive to conventional treatments, novel therapies are needed to improve disease outcomes. Multiple novel therapies primarily targeting angiogenesis have entered clinical trials for metastatic thyroid carcinoma. Partial response rates up to 30% have been reported in single agent studies, but prolonged disease stabilization is more commonly seen. The most successful agents target the vascular endothelial growth factor receptors, with potential targets including the mutant kinases associated with papillary and medullary oncogenesis. Two drugs approved for other malignancies, sorafenib and sunitinib, have had promising preliminary results reported, and are being used selectively for patients who do not qualify for clinical trials. Additional agents targeting tumor vasculature, nuclear receptors, epigenetic abnormalities, and the immune response to neoplasia have also been investigated. Randomized trials for several agents are underway that may lead to eventual drug approval for thyroid cancer. Treatment for patients with metastatic or advanced thyroid carcinoma now emphasizes clinical trial opportunities for novel agents with considerable promise. Alternative options now exist for use of tyrosine kinase inhibitors that are well tolerated and may prove worthy of regulatory approval for this disease.

Tyrosine kinase inhibitors and the thyroid

Protein tyrosine kinase inhibitors (TKIs) have emerged as significant targets for novel cancer therapies. For patients with differentiated or medullary carcinomas unresponsive to conventional treatments, multiple novel therapies primarily targeting angiogenesis have entered clinical trials. Partial response rates up to 30% have been reported in single-agent studies, but prolonged disease stabilisation is more commonly seen. The most successful agents target the vascular endothelial growth factor receptors. Sorafenib and sunitinib have had promising preliminary results reported and are being used selectively for patients who do not qualify for clinical trials. Treatment for patients with metastatic or advanced thyroid carcinoma now emphasises clinical trial opportunities for novel agents with considerable promise. Adverse effects on thyroid function and thyroid hormone metabolism have also been seen with several TKIs, necessitating prospective thyroid function testing for all patients starting therapy.

Targeting the RET pathway in thyroid cancer

The RET (rearranged during transfection) protooncogene encodes a single pass transmembrane receptor that is expressed in cells derived from the neural crest and the urogenital tract. As part of a cell-surface complex, RET binds glial derived neurotrophic factor (GDNF) ligands in conjunction with GDNF-family alpha co-receptors (GFRalpha). Ligand-induced activation induces dimerization and tyrosine phosphorylation of the RET receptor with downstream activation of several signal transduction pathways. Activating germline RET mutations play a central role in the development of the multiple endocrine neoplasia (MEN) syndromes MEN2A, MEN2B, and familial medullary thyroid carcinoma (FMTC) and also in the development of the congenital abnormality Hirschsprung's disease. Approximately 50% of patients with sporadic MTC have somatic RET mutations, and a significant portion of papillary thyroid carcinomas result from chromosomal inversions or translocations, which activate RET (RET/PTC oncogenes). The RET protooncogene has a significant place in cancer prevention and treatment. Timely thyroidectomy in kindred members who have inherited a mutated RET allele, characteristic of MEN2A, MEN2B, or FMTC, can prevent MTC, the most common cause of death in these syndromes. Also, recently developed molecular therapeutics that target the RET pathway have shown activity in clinical trials of patients with advanced MTC, a disease for which there has been no effective therapy.