patient and the maturity of the germ cell when the malignancy begins During embryonic development, germ cells migrate to the gonads, but aberrant migration in the setting of malignancy can lead to extragonadal germ cell tumors This section will focus on tumors located within the gonads themselves Tumors of the ovary are rare and account for only 1% of pediatric cancers overall While they may occur at any age, the incidence begins to increase at to years and peaks at 19 years of age Two-thirds of pediatric ovarian tumors are germ cell tumors Abdominal pain is the most common presenting symptom, occurring in 80% of patients Pain may be chronic or acute, mimicking an acute abdomen, as the tumor can cause ovarian torsion Other presenting signs and symptoms include a palpable abdominal mass, bowel or bladder dysfunction, or menstrual changes Some ovarian tumors may cause precocious puberty or virilization If a patient has a known or possible ovarian mass, the history and physical examination should include a thorough menstrual history as well as assessment of any virilization or precocious puberty The differential diagnosis should include benign etiologies, such as an ovarian cyst Laboratory evaluation should include a CBC, chemistries, quantitative beta human chorionic gonadotropin (β-HCG), AFP, LDH, and CA-125 Ultrasound can clarify whether the tumor is cystic or solid as well as location Further imaging should generally be carried out in conjunction with the managing oncologist or surgeon and rarely needs to be performed in the ED Malignant masses are most commonly germ cell derived Of these, the more common are dysgerminoma, which may be bilateral in 20% of cases, and endodermal sinus tumor (yolk sac tumor), which presents with an elevated AFP Malignant tumors may also be derived from nongerm cell ovarian tissue or from nonovarian tissues, as is the case for ovarian involvement in leukemia or lymphoma Tumors of the testicle are rare and account for only 2% of solid neoplasms in boys While they may occur at any age, testicular tumors seen in adolescents are similar to those found in adults Prepubertal boys have tumors with unique clinical manifestations and different prognostic implications The major risk factor for the development of a testicular tumor is the presence of an undescended testicle, even after repair Approximately 75% of pediatric testicular tumors are germ cell tumors (as compared with more than 90% in the adult population) Testicular tumors commonly present as an enlarged testicle or as irregular, nontender scrotal masses that not transilluminate They may have minimal or no associated symptoms, which may delay the diagnosis At the time of diagnosis, 20% of patients will also have an inguinal hernia and another 20% will have a hydrocele About 75% of these tumors are localized at diagnosis, but sites of potential metastases include retroperitoneal lymph nodes and the chest