Medullary ca of thyroid is associated with increase in
## **Core Concept**
Medullary carcinoma of the thyroid (MTC) is a type of thyroid cancer that originates from the parafollicular cells, also known as C cells, which produce **calcitonin**. This cancer is associated with specific biochemical markers and genetic mutations, notably in the **RET proto-oncogene**.
## **Why the Correct Answer is Right**
Medullary thyroid carcinoma is characterized by an overproduction of **calcitonin**, a hormone normally produced by the C cells of the thyroid gland. Elevated calcitonin levels are a diagnostic hallmark and are used as a tumor marker for MTC. The RET proto-oncogene mutations are also commonly associated with MTC, but the question specifically asks about a biochemical increase.
## **Why Each Wrong Option is Incorrect**
- **Option A:** While certain thyroid cancers can lead to increased levels of thyroid hormones or their metabolites, medullary carcinoma of the thyroid does not directly cause an increase in thyroid hormones like T3 or T4; it originates from C cells, not follicular cells.
- **Option B:** Chromogranin A is a marker that can be elevated in various neuroendocrine tumors, including medullary thyroid carcinoma. However, it is not as specific for MTC as calcitonin.
- **Option D:** Carcinoembryonic antigen (CEA) can be elevated in medullary thyroid carcinoma but is not as specific or sensitive as calcitonin for diagnosing MTC.
## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that **calcitonin** levels are used not only for diagnosing medullary thyroid carcinoma but also for monitoring disease recurrence. Additionally, genetic screening for **RET proto-oncogene** mutations is crucial in familial cases of MTC.
## **Correct Answer:** . **Calcitonin**