Radioactive iodine is effective treatment for metastatic lung disease for which of the following thyroid neoplasms?

b. Papillary carcinoma

c. Follicular carcinoma

Radioactive iodine is used only in patients who have differentiated thyroid carcinomas. It is of no value in the treatment and follow-up of patients with Hürthle cell, medullary or anaplastic carcinomas. Most papillary carcinomas are capable of taking up radioactive iodine. Most papillary carcinomas in patients under 50-years of age do so, providing that the patient has had a total thyroidectomy and there is no normal thyroid tissue to compete for the 131I. About 20% of all papillary carcinomas do not trap sufficient iodine for imaging or therapy. These are usually patients with papillary carcinoma variants: a tall cell variant of papillary carcinoma, insular carcinoma, or clear cell carcinoma.

Nearly all metastatic follicular carcinomas retain the ability to trap 131I sufficiently for imaging and for therapy. Even welldifferentiated papillary and follicular carcinoma cannot compete successfully for 131I with normal thyroid tissue and unless this has been removed or subsequently ablated with an initial dose of 131I, many metastases cannot be detected or treated.