Challenges in diagnosis of primary penile tumor of the endodermal sinus in infants

Germ cell tumors (GCTs) are an uncommon group of malignant neoplasms in the pediatric population. The endodermal sinus tumor, also known as yolk sac tumor, is the most frequent subtype of GCT and typically originates in the gonads. Extragonadal presentation is rare, particularly in the penis.

To describe the case of a male infant with an extragonadal penile endodermal sinus tumor, emphasizing the diagnostic challenges and the role of alpha-fetoprotein (αFP) as a monitoring biomarker.

A previously healthy 18-month-old male infant presented with a one-month history of a left inguinoscrotal mass. Imaging revealed a tumor arising from the corpus cavernosum with inguinal extension. The initial αFP level was 4,396 ng/mL. Endodermal sinus tumor with pulmonary metastasis (stage IV) was confirmed. A macroscopically complete surgical resection was performed, preserving penile and testicular structures, followed by six cycles of chemotherapy with bleomycin, etoposide, and carboplatin. αFP levels decreased progressively (2,325 ng/mL at 2 days, 103 ng/mL at 4 weeks, 12.21 ng/mL at the end of treatment, and 6.9 ng/mL at 6 months). At 12 months of follow-up, the patient remained disease-free, with normal psychomotor development and preserved urinary function.

Extragonadal penile localization of endodermal sinus tumor is rare but has a favorable prognosis when treated with conservative management and chemotherapy. aFP is a useful marker for both diagnosis and follow-up.