All of the following are true about medullary carcinoma of thyroid except
**Core Concept**
Medullary thyroid carcinoma (MTC) is a type of thyroid cancer that originates from the parafollicular cells, also known as C cells. These cells are responsible for producing calcitonin, a hormone involved in calcium homeostasis. MTC is often associated with genetic mutations, particularly in the RET proto-oncogene.
**Why the Correct Answer is Right**
Medullary thyroid carcinoma typically presents with an elevated calcitonin level, which serves as a tumor marker for this disease. The tumor cells in MTC produce and secrete calcitonin, leading to its elevated levels in the blood. Additionally, MTC can be associated with multiple endocrine neoplasia (MEN) syndromes, such as MEN 2A and MEN 2B, which are characterized by the presence of other endocrine tumors.
**Why Each Wrong Option is Incorrect**
**Option A:** MTC is not typically associated with radiation exposure, unlike other types of thyroid cancer such as papillary thyroid carcinoma. Radiation exposure is a known risk factor for papillary thyroid carcinoma but not for medullary thyroid carcinoma.
**Option B:** MTC can metastasize to lymph nodes and distant organs, such as the lungs and bones. However, it is not typically associated with lymph node metastasis at presentation, unlike other types of thyroid cancer. MTC often presents with advanced disease, including lymph node and distant metastases.
**Option C:** MTC is indeed a type of thyroid cancer that is resistant to radioactive iodine therapy. This is because the tumor cells in MTC do not take up radioactive iodine, which is used to treat other types of thyroid cancer.
**Clinical Pearl / High-Yield Fact**
It is essential to remember that MTC can be associated with familial syndromes, such as MEN 2A and MEN 2B, which are characterized by the presence of other endocrine tumors. Therefore, patients with a family history of MTC or other endocrine tumors should be screened for these syndromes.
**Correct Answer: B. MTC often presents with advanced disease, including lymph node and distant metastases.**