All of the following are true regarding medullary carcinoma of thyroid except: March 2010
**Core Concept**
Medullary carcinoma of the thyroid (MTC) is a rare, malignant tumor originating from the parafollicular cells (also known as C-cells) of the thyroid gland. This type of cancer is associated with the MEN2 syndrome and is often characterized by the presence of calcitonin, a hormone produced by C-cells.
**Why the Correct Answer is Right**
Medullary carcinoma of the thyroid is indeed associated with the MEN2 syndrome, which is a genetic disorder that predisposes individuals to multiple endocrine tumors, including MTC. The tumor cells of MTC produce calcitonin, which can be used as a tumor marker for diagnosis and follow-up. Additionally, MTC is often calcitonin-producing and lacks the typical thyroid follicular architecture.
**Why Each Wrong Option is Incorrect**
**Option A:** MTC is not typically associated with radiation exposure.
**Option B:** MTC is not usually treated with radioactive iodine, as it does not take up iodine like other thyroid cancers.
**Option C:** MTC is not a type of papillary thyroid carcinoma, but rather a distinct type of thyroid cancer originating from C-cells.
**Clinical Pearl / High-Yield Fact**
MTC is often diagnosed incidentally in patients undergoing imaging studies for other reasons, and the presence of calcitonin in the serum can aid in its diagnosis.
**Correct Answer: C. MTC is not a type of papillary thyroid carcinoma, but rather a distinct type of thyroid cancer originating from C-cells.**