**Core Concept**
Seminomas and nonseminomatous germ cell tumors (NSGCTs) are types of testicular cancer with distinct clinicopathologic features. Seminomas are typically radiosensitive and have a better prognosis compared to NSGCTs.

**Why the Correct Answer is Right**
Seminomas often present with a higher mean age at diagnosis, usually above 40 years, whereas NSGCTs tend to occur in younger men. Additionally, seminomas are more commonly associated with elevation of human chorionic gonadotropin (hCG) levels, although beta-hCG levels are usually lower in seminomas. Furthermore, seminomas have a higher likelihood of being confined to the testis (stage I) at diagnosis, which contributes to their better prognosis.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is not a distinguishing feature between seminomas and NSGCTs. Both types of tumors can exhibit lymphovascular invasion, which is a marker of aggressive disease.
**Option B:** This option is incorrect because hCG levels are indeed elevated in both seminomas and NSGCTs, but to a lesser extent in seminomas. Beta-hCG is often used as a tumor marker in both types of tumors.
**Option C:** This option is incorrect because both seminomas and NSGCTs can present with a painless testicular mass, which is the most common presenting symptom of testicular cancer.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that NSGCTs are more likely to present with a palpable abdominal mass or symptoms related to metastatic disease, such as pain or weight loss, due to their propensity for distant metastasis.

**Correct Answer: D.**