Ahmet Fatih YILMAZ, Muammer BÜYÜKİNAN, Buket KARA, Hıdır ESME
The Turkish Journal of Pediatrics - 2026;68(5):889-895
Background. Gonadotropin-releasing hormone-independent precocious puberty (GnRH-independent PP) due to a human chorionic gonadotropin (hCG)-secreting mediastinal germ cell tumor is an exceptionally rare presentation, particularly in the context of Klinefelter syndrome. This case highlights the diagnostic challenges posed by GnRH-independent PP and underscores the importance of considering extragonadal germ cell tumors in the differential diagnosis of virilization with suppressed gonadotropins. Case Presentation. A 7-year-9-month-old boy presented with rapidly progressive virilization, including pubic hair development, penile enlargement, and voice deepening. Laboratory evaluation revealed markedly elevated testosterone, estradiol, beta-hCG, and alpha-fetoprotein (AFP) levels, with suppressed gonadotropins and a prepubertal GnRH stimulation response. Imaging studies demonstrated a large anterior mediastinal mass containing fat and calcifications, while scrotal ultrasonography showed no testicular lesion. The mediastinal mass was completely resected and histopathology confirmed a mixed germ cell tumor composed of seminoma, yolk sac tumor, and Grade II immature teratoma with beta-hCG-positive trophoblastic foci. Karyotype analysis revealed 47,XXY, consistent with Klinefelter syndrome. Following surgery and four cycles of bleomycin, etoposide, and cisplatin (BEP) chemotherapy, tumor markers normalized rapidly, and no recurrence was detected during long-term follow-up. Conclusions. This case illustrates a rare presentation of GnRH-independent PP due to a beta-hCG-secreting mediastinal mixed germ cell tumor in a child with previously undiagnosed Klinefelter syndrome. Routine karyotype analysis should be considered in male patients with mediastinal germ cell tumors. In children presenting with unexplained virilization and suppressed gonadotropins, extragonadal germ cell tumors and their biochemical markers (beta-hCG, AFP) must be carefully evaluated. Early recognition, timely surgical intervention, metabolic monitoring, and multidisciplinary care are critical for optimizing outcomes.
