**Core Concept**
Squamous cell carcinoma (SCC) is a type of skin cancer characterized by the uncontrolled growth of squamous cells, which are the flat cells on the surface of the skin. The prognosis of SCC depends on various factors, including the location, depth of invasion, and lymph node involvement.

**Why the Correct Answer is Right**
The best prognosis is associated with **well-differentiated SCC**, particularly when it occurs on the **ear or lip**. This is because these sites have a lower risk of lymph node metastasis due to the presence of a rich blood supply, which facilitates early detection and treatment. Additionally, well-differentiated SCC tends to grow more slowly and is more likely to be cured with local treatment.

**Why Each Wrong Option is Incorrect**
* **Option A:** SCC on the trunk or extremities has a worse prognosis due to a higher risk of lymph node metastasis.
* **Option B:** Moderately or poorly differentiated SCC has a worse prognosis due to a higher risk of lymph node metastasis and recurrence.
* **Option C:** SCC with lymph node involvement has a worse prognosis due to the increased risk of distant metastasis.

**Clinical Pearl / High-Yield Fact**
When evaluating a patient with SCC, it's essential to assess the tumor's location, differentiation, and depth of invasion to determine the prognosis and plan appropriate treatment.

**Correct Answer:** C. Moderately or poorly differentiated SCC has a worse prognosis due to a higher risk of lymph node metastasis and recurrence.