**Question:** Follicular carcinoma of thyroid is due to mutation of:

A. RET proto-oncogene
B. BRAF proto-oncogene
C. RAS proto-oncogene
D. PAX8/PPARγ gene fusion

**Core Concept:**

Follicular carcinoma of the thyroid is a type of thyroid cancer that arises from the follicular cells, which are responsible for producing thyroid hormones. In these cells, mutations in specific genes can lead to uncontrolled cell growth and the development of cancer. The correct answer refers to a specific gene mutation that contributes to the pathogenesis of follicular thyroid carcinoma.

**Why the Correct Answer is Right:**

Follicular carcinoma of the thyroid is primarily due to mutations in the RET proto-oncogene (Rearranged during Transfection). The RET gene is located on chromosome 10 and encodes a receptor tyrosine kinase, which is involved in cell signaling pathways that regulate cell growth, differentiation, and survival. Mutations in this gene can lead to the production of an abnormal protein, which disrupts normal cell signaling and promotes uncontrolled cell growth, ultimately causing thyroid cancer.

**Why Each Wrong Option is Incorrect:**

A. RET proto-oncogene (Correct): This option is correct because mutations in the RET proto-oncogene are known to cause thyroid cancer, particularly follicular carcinoma.

B. BRAF proto-oncogene (Incorrect): While BRAF mutations are associated with other types of cancer, they are not primarily responsible for thyroid cancer, specifically follicular carcinoma.

C. RAS proto-oncogene (Incorrect): Mutations in the RAS proto-oncogene are typically associated with other types of cancer, not specifically follicular carcinoma of the thyroid.

D. PAX8/PPARγ gene fusion (Incorrect): This option refers to a specific genetic rearrangement that occurs in a subset of thyroid cancer cases, but it is not the primary driver mutation for thyroid cancer in general or follicular carcinoma specifically.

**Clinical Pearl:**

Understanding the genetic basis of cancer is crucial for understanding disease pathogenesis and treatment strategies. Identifying the specific mutations involved in thyroid cancer can help guide targeted therapies, which are more effective and have fewer side effects compared to conventional chemo- and radiotherapy. Therefore, knowing the key genetic mutations in thyroid cancer can significantly impact patient management and prognosis.