**Core Concept**
Anaplastic thyroid carcinoma (ATC) is a rare and aggressive type of thyroid cancer characterized by rapid growth and invasion of surrounding tissues. It is often associated with advanced age and poor prognosis.

**Why the Correct Answer is Right**
The correct answer options (ade) accurately describe ATC. **Option A: Common in elderly** is true, as ATC typically affects individuals over the age of 60. **Option D: Distant metastasis common** is also correct, as ATC often spreads to distant sites, including the lungs, bones, and brain. **Option E: Some degree of differentiation to Papillary and Follicular types seen** is true, as ATC may exhibit some degree of differentiation to other thyroid cancer types, such as papillary or follicular carcinoma.

**Why Each Wrong Option is Incorrect**
**Option B: Well encapsulated** is incorrect, as ATC is often poorly encapsulated and invades surrounding tissues, including the trachea, esophagus, and major blood vessels. **Option C: Will not invade surrounding structures** is incorrect, as ATC is known for its aggressive invasion of surrounding structures.

**Clinical Pearl / High-Yield Fact**
ATC is often associated with a history of radiation exposure, thyroiditis, or previous thyroid surgery. A high index of suspicion and prompt diagnosis are critical for improving outcomes in patients with ATC.

**✓ Correct Answer: C. ade**