A 23-year-old man is being evaluated for the new development of a nodule in his neck. Physical examination finds a 3.5-cm thyroid nodule. The lesion is removed surgically, and histologic sections reveal groups of poorly differentiated tumors cells within a stroma with large areas of amyloid. This familial form of this type of malignancy is associated with abnormalities of which of the following protooncogenes

**Core Concept**
The question is testing knowledge of a specific familial form of thyroid cancer characterized by its association with a genetic abnormality. This cancer type is known for its aggressive behavior and distinctive histological features, including the presence of amyloid in the stroma.

**Why the Correct Answer is Right**
The familial form of thyroid cancer described in the question is Medullary Thyroid Carcinoma (MTC). MTC is associated with mutations in the RET protooncogene, which encodes a receptor tyrosine kinase involved in cell signaling. These mutations lead to the activation of the RET protein, resulting in uncontrolled cell growth and tumor formation. The presence of amyloid in the stroma is a hallmark feature of MTC, distinguishing it from other types of thyroid cancer.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the familial form of Papillary Thyroid Carcinoma is associated with mutations in the BRAF gene, not a protooncogene related to MTC.
**Option B:** This option is incorrect because the familial form of Follicular Thyroid Carcinoma is associated with mutations in the RAS gene, not a protooncogene related to MTC.
**Option C:** This option is incorrect because the familial form of Anaplastic Thyroid Carcinoma is associated with mutations in the p53 gene, not a protooncogene related to MTC.

**Clinical Pearl / High-Yield Fact**
Medullary Thyroid Carcinoma is a rare but aggressive form of thyroid cancer that can be associated with familial syndromes, including Multiple Endocrine Neoplasia type 2 (MEN2). Early detection and treatment of MTC are critical to improve patient outcomes.

**Correct Answer:** C. RET protooncogene

✓ Correct Answer: B. ret