The FDA ( Food and Drug Administration ) has granted Orphan Drug Designation for the investigational MEK 1/2 inhibitor, Selumetinib for adjuvant treatment of patients with stage III or IV differentiated thyroid cancer.

Cancer of the thyroid gland is diagnosed in approximately 60,000 people in the US each year. Nearly 95% of patients have differentiated tumours with an associated five-year survival of over 90%. Differentiated thyroid cancer is usually treated by surgery and thyroxine hormone replacement therapy, and radioactive iodine treatment ( RAI ) is recommended for patients with known / suspected metastases at diagnosis and for those at high risk of recurrence.
Up to 30% of patients experience recurrence of differentiated thyroid cancer after initial treatment.

Approximately 5-15% of patients with differentiated thyroid cancer do not respond to RAI. Ten year survival in patients who fail to take up radioactive iodine into tumour cells is 10% compared to nearly 60% in those with normal uptake.
Traditional chemotherapy has minimal efficacy in patients with metastatic differentiated thyroid cancer.

Selumetinib is an oral, potent, selective inhibitor of MEK, part of the mitogen-activated protein kinase ( MAPK ) pathway which is frequently activated in cancer, including those with the KRAS mutation, which is present in 20% of human cancers and 20-30% of non-small cell lung cancer tumours.
MAPK activation also inhibits expression of thyroid hormone biosynthesis genes, including the sodium/iodine symporter ( NIS ) which facilitates iodine uptake into cells.
Pre-clinical studies have suggested that following MAPK inhibition, iodine uptake by thyroid tumour cells is regained. ( Xagena )

Source: AstraZeneca, 2016