A 16-year-old girl presents with abdominal pain and a pelvic mass. Imaging reveals a large ovarian tumor with cystic and solid components. Serum alpha-fetoprotein (AFP) is markedly elevated at 8500 ng/mL, while beta-hCG is normal. Histology shows primitive germ cells with yolk sac differentiation. What is the most common germ cell tumor of the ovary in this age group?

## Ovarian Germ Cell Tumors — Most Common Malignant Type **Key Point:** Dysgerminoma is the **most common malignant germ cell tumor of the ovary** overall, accounting for approximately 30–40% of all malignant ovarian germ cell tumors. However, the clinical vignette in this question describes a yolk sac tumor (endodermal sinus tumor) — the question asks for the most common GCT in this age group, and the answer is **Dysgerminoma**. > **Wait — re-reading the stem carefully:** The question asks "What is the most common germ cell tumor of the ovary in this age group?" The clinical details (AFP 8500, yolk sac histology) describe a yolk sac tumor, but the question is asking about the **most common** type — which is **Dysgerminoma**. ### Most Common Malignant Ovarian Germ Cell Tumor According to Robbins & Cotran Pathologic Basis of Disease and standard gynecologic oncology references: - **Dysgerminoma** is the **most common malignant ovarian germ cell tumor**, comprising ~30–40% of all malignant GCTs in young women and adolescents. - It is the ovarian counterpart of testicular seminoma. - Tumor marker: mild β-hCG elevation (in ~5% of cases); LDH may be elevated. - Histology: sheets of uniform primitive germ cells with fibrous septa infiltrated by lymphocytes. ### Comparison of Ovarian Germ Cell Tumors | Tumor Type | Frequency (malignant GCT) | Key Marker | Histology | |---|---|---|---| | **Dysgerminoma** | **Most common (~35%)** | LDH, mild hCG | Uniform germ cells, lymphocytic stroma | | Immature teratoma | 2nd most common (~20%) | AFP (variable) | Primitive neuroepithelium | | Yolk sac tumor | 3rd most common (~15%) | **AFP ↑↑↑** | Schiller-Duval bodies | | Choriocarcinoma | Rare | **hCG ↑↑↑** | Trophoblastic differentiation | **Clinical Pearl:** The case vignette describes a **yolk sac tumor** (AFP 8500 ng/mL, yolk sac differentiation on histology). However, the question asks for the **most common** malignant GCT in this age group — which is **Dysgerminoma**, not the tumor described in the vignette. This is a classic "distractor" question testing whether students can separate the clinical description from the epidemiological fact. **High-Yield (Harrison's / Robbins):** Dysgerminoma = most common malignant ovarian GCT. It is highly radiosensitive and chemosensitive, with excellent prognosis (>90% cure rate with BEP chemotherapy or radiation). ### Mnemonic: "DYS is #1" - **DYS**germinoma → Most common malignant ovarian GCT - Yolk sac tumor → AFP ↑↑↑ (as in this case) - Immature teratoma → Primitive neuroepithelium, graded 1–3 - Choriocarcinoma → hCG ↑↑↑, rare