A 22-year-old woman undergoes surgery for a right ovarian mass. Pathology shows a solid tumor with sheets of large, clear cells with central nuclei, resembling seminoma. No Schiller-Duval bodies or glandular differentiation is seen. Serum AFP and β-hCG are both negative. Which feature best distinguishes this dysgerminoma from yolk sac tumor?

Explanation

## Discriminating Feature: Absence of Tumor Marker Elevation ### Dysgerminoma vs. Yolk Sac Tumor | Feature | Dysgerminoma | Yolk Sac Tumor | |---------|---|---| | **Tumor markers** | AFP negative; β-hCG negative (or trace in mixed tumors) | **AFP markedly elevated** (hallmark) | | **Histology** | Uniform sheets of large clear cells; seminoma-like | Glandular, microcystic, **Schiller-Duval bodies** | | **Bilaterality** | 10–15% | <5% (rare) | | **Age** | Adolescents/young adults (15–20 years) | Adolescents/young adults (16–20 years) | | **Chemosensitivity** | Excellent (BEP) | Excellent (BEP) | | **Radiosensitivity** | Excellent | Moderate | | **Ovarian dysgenesis association** | Yes (XY karyotype, streak gonads) | No | **Key Point:** The **absence of AFP and β-hCG elevation** is the best distinguishing feature of dysgerminoma from yolk sac tumor in this clinical context. Yolk sac tumor (endodermal sinus tumor) is defined by **markedly elevated serum AFP**, which serves as both a diagnostic marker and a tool for monitoring treatment response. Dysgerminoma, by contrast, does not produce AFP; it may rarely produce trace β-hCG in mixed tumors, but pure dysgerminoma is marker-negative. This is the single most clinically actionable discriminator between the two tumors (Robbins & Cotran Pathologic Basis of Disease, 10th ed.). **Clinical Pearl:** The stem explicitly states AFP and β-hCG are both negative — this is the defining feature that clinches dysgerminoma over yolk sac tumor. Option A (Schiller-Duval bodies) is a histologic feature of yolk sac tumor, not dysgerminoma, so its *absence* in this case is consistent with dysgerminoma but does not "distinguish" dysgerminoma from yolk sac tumor as a positive feature of dysgerminoma. Option B (bilaterality 10–15%) is a feature of dysgerminoma, but yolk sac tumor is also predominantly unilateral — this is a less sharp discriminator. Option D (BEP response) is shared by both tumors and is therefore not a distinguishing feature. **High-Yield:** - **Yolk sac tumor** → AFP markedly elevated (most reliable marker); Schiller-Duval bodies on histology - **Dysgerminoma** → AFP and β-hCG negative; seminoma-like histology; LDH and PLAP may be elevated - Negative AFP in a germ cell tumor strongly favors dysgerminoma over yolk sac tumor - Both respond excellently to BEP chemotherapy — chemosensitivity does NOT distinguish them **Mnemonic: AFP = Away From Pure dysgerminoma** - AFP is the hallmark of Yolk Sac Tumor, NOT dysgerminoma - Negative AFP + seminoma-like histology = Dysgerminoma