Beyond RET: potential therapeutic approaches for advanced and metastatic medullary thyroid carcinoma

Medullary thyroid carcinoma (MTC) is a rare calcitonin-producing neuroendocrine tumour that originates from the parafollicular C-cells of the thyroid gland. The RET proto-oncogene encodes the RET receptor tyrosine kinase, which has essential roles in cell survival, differentiation and proliferation. Activating mutations of RET are associated with the pathogenesis of MTC and have been demonstrated in nearly all hereditary and in 30-50% of sporadic MTC cases, making this receptor an excellent target for small-molecule inhibitors for this tumour. Clinical trials of small organic inhibitors of tyrosine kinase receptors (TKIs) targeting the RET receptor have shown efficacy for treatment of metastatic MTC with 30-50% of patients responding to these agents. Despite the importance of the RET receptor in MTC, it is clear that other signal transduction pathways, tyrosine kinase receptors, and tumour suppressor genes are involved in MTC tumourigenesis and progression. A better understanding of molecular cross-talk between these signal pathways and the RET receptor may lead to combinatorial therapy that will improve outcomes beyond what is currently possible with RET-directed TKIs. Finally, there is evidence that immunological-based therapy using dendritic cell vaccination strategies have been effective for reducing tumour mass in a small number of patients. The identification of additional MTC-specific tumour antigens and a better understanding of specific epitopes in these tumour antigens may lead to improvement of response rates.

New agents in the treatment for malignancies of the salivary and thyroid glands

The treatment of relatively rare malignancies, such as those of the salivary glands and iodine refractory thyroid cancer, has been invigorated by the development of novel molecular targeting agents. Accrual to clinical trials for these disease sites continues to be limited by their relatively low incidence. Nonetheless, multicenter collaborations have contributed greatly to the development of a number of emerging systemic therapies. This article briefly summarizes the epidemiology and pathogenesis of salivary gland and thyroid cancer, and then describes some of the new drugs under evaluation for these malignancies.