Screening method for medullary carcinoma thyroid is
**Core Concept**
Medullary carcinoma of the thyroid (MTC) is a rare, neuroendocrine tumor originating from the parafollicular cells (also known as C cells) of the thyroid gland. Early detection and screening are crucial for improving outcomes in patients with familial or sporadic MTC.
**Why the Correct Answer is Right**
The correct answer is related to the genetic basis of MTC. Mutations in the RET proto-oncogene are responsible for the development of MTC in approximately 25% of cases. The RET proto-oncogene is a receptor tyrosine kinase that plays a critical role in the signaling pathway of the glial cell line-derived neurotrophic factor (GDNF) family of ligands. Screening for MTC is typically performed in individuals with a family history of the disease or those with a known RET mutation.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not address the genetic basis of MTC. While thyroid-stimulating hormone (TSH) levels can be used to screen for thyroid cancer, it is not a specific marker for MTC.
**Option B:** This option is incorrect because calcitonin is a marker for MTC, but it is not a screening method. Elevated calcitonin levels can indicate the presence of MTC, but they are not used to screen the general population.
**Option C:** This option is incorrect because ultrasound is a diagnostic tool used to visualize thyroid nodules and tumors, but it is not a screening method for MTC.
**Clinical Pearl / High-Yield Fact**
Familial MTC is often associated with multiple endocrine neoplasia type 2 (MEN2) syndromes, which also include pheochromocytoma and hyperparathyroidism. Genetic testing for RET mutations is essential for identifying individuals at risk of developing MTC.
**Correct Answer: B. Calcitonin is a marker for MTC, but it is not a screening method.**