**Question:** Most common ovarian tumor in less than 20 years is:

A. Germ cell tumors
B. Stromal cell tumors
C. Epithelial tumors
D. Mixed tumors

**Core Concept:** Ovarian tumors are a diverse group of neoplastic conditions arising from various cell types within the ovary. These tumors can be broadly classified into germ cell, stromal cell, epithelial, and mixed tumors based on cell of origin.

**Why the Correct Answer is Right:** In females under 20 years, germ cell tumors are the most common ovarian tumors. Germ cell tumors arise from primordial germ cells and can be further classified into mature teratomas, immature teratomas, dysgerminomas, and non-seminomatous germ cell tumors (NSGCTs). These tumors are often seen in the first two decades of life, particularly in individuals with Klinefelter's syndrome or Turner's syndrome.

**Why Each Wrong Option is Incorrect:**

A. Stromal cell tumors are less common than germ cell tumors in this age group. Stromal cell tumors originate from cells within the ovarian stroma and can be further categorized into granulosa cell tumors, theca cell tumors, and mixed tumors.

B. Epithelial tumors are relatively rare in females under 20 years. These tumors originate from cells lining the fallopian tubes or the surface epithelium of the ovary.

C. Mixed tumors are combinations of two or more types of ovarian neoplasms. While mixed tumors can occur in younger females, they are less common than germ cell tumors.

D. Germ cell tumors are more prevalent in females under 20 years, as mentioned above.

**Clinical Pearl:** A thorough understanding of ovarian tumor types and their characteristics is crucial for accurate diagnosis and appropriate management of young females presenting with adnexal masses.

**Correct Answer:** D. Germ cell tumors are the most common ovarian tumors in females under 20 years. These tumors arise from primordial germ cells and can be further classified into mature teratomas, immature teratomas, dysgerminomas, and non-seminomatous germ cell tumors (NSGCTs).