**Core Concept:** Testicular tumors are neoplasms that originate from germ cells or Sertoli and Leydig cells within the testes. They can be benign (e.g., teratomas) or malignant (e.g., seminomas and non-seminomas), and can be detected through appropriate markers or biomarkers.

**Why the Correct Answer is Right:** Alpha-fetoprotein (AFP) is a protein produced during fetal life and is considered a marker for germ cell tumors, particularly in patients with non-seminoma. The correct answer is C. AFP is elevated in about 10% of testicular tumors and is elevated in patients with non-seminoma. This is because non-seminomas, including embryonal carcinomas, are known to produce AFP.

**Why Each Wrong Option is Incorrect:** Option A (β-HCG) is a marker for germ cell tumors but is more commonly associated with seminoma, not non-seminoma. Option B (LDH) is a general tumor marker that can be elevated in various cancers, but it is not specific for testicular tumors. Option D (CA-125) is a marker for ovarian cancer and other malignancies, not testicular tumors.

**Why AFP is Right:** The correct answer, AFP, is a specific marker for non-seminoma germ cell tumors, helping clinicians differentiate between seminomas and non-seminomas in patients with elevated tumor markers.

**Clinical Pearl:** In cases with elevated tumor markers, understanding the specific markers for different types of tumors is crucial for accurate diagnosis and appropriate management strategies. AFP, β-HCG, LDH, and CA-125 are essential tumor markers that help diagnose and monitor various cancers.

**Correct Answer:** C. Alpha-Fetoprotein (AFP)