**Core Concept**
Small cell carcinoma of the lung is a highly aggressive and malignant tumor type that often presents with advanced disease. It is characterized by its rapid growth rate and early metastasis to regional lymph nodes and distant sites, including the mediastinum.

**Why the Correct Answer is Right**
Small cell carcinoma is the most common primary malignancy causing superior vena cava (SVC) syndrome. This is due to its propensity to invade and compress the SVC, which is a major venous structure in the thorax. The tumor's aggressive nature and early metastasis allow it to grow and compress the SVC, leading to the classic symptoms of SVC syndrome, including facial swelling, arm edema, and shortness of breath. The SVC is particularly susceptible to compression by small cell carcinoma due to its location in the mediastinum and the tumor's tendency to grow in a central location.

**Why Each Wrong Option is Incorrect**
**Option A:** Lymphoma can cause SVC syndrome, but it is less common than small cell carcinoma. Lymphoma tends to present with more systemic symptoms and may not grow as rapidly as small cell carcinoma, leading to slower compression of the SVC.

**Option C:** Non-small cell carcinoma (NSCLC) is the most common type of lung cancer, but it is less likely to cause SVC syndrome than small cell carcinoma. NSCLC tends to grow more slowly and is less aggressive than small cell carcinoma, making it less likely to compress the SVC.

**Option D:** Metastasis to the SVC can occur from various primary tumors, including breast and lung cancer. However, metastatic disease to the SVC is less common than primary small cell carcinoma and may not present with the same classic symptoms of SVC syndrome.

**Clinical Pearl / High-Yield Fact**
SVC syndrome is a medical emergency that requires prompt diagnosis and treatment. The symptoms of SVC syndrome can be reversed with prompt treatment, but delayed diagnosis can lead to significant morbidity and mortality.

**✓ Correct Answer: B. Small cell carcinoma**