SUN-178 Contrasting Clinical Presentations of Pediatric Leydig Cell Tumors: Two Cases with Unique Features

Abstract Disclosure: J. Winer: None. I. Marranzini Rodriguez: None. M. Lemelman: None. D. Deplewski: None. S.W. Greeley: None. Introduction: Testicular tumors are rare in pediatrics, accounting for 1% of solid tumors, with Leydig cell tumors comprising approximately 4% of cases. These testosterone-producing neoplasms typically present with peripheral precocious puberty, but they may induce central puberty which can complicate the diagnosis. Here we present two cases of this rare tumor, highlighting different presentations. Description of cases: Our first case presented at 2 years and 11 months with precocious puberty. His exam was notable for left testis long axis diameter of 3 cm and volume of 5 mL (compared 2 cm and 3 mL on the right), phallus length of 10 cm, Tanner 3 pubic hair. Bone age was advanced to 6 years. Laboratory evaluation showed an LH 0.3 mIU/mL (< 0.3), FSH <0.3 mIU/mL (< 1.0), hCG < 2.0 (< 2.0), total testosterone 835 ng/dL (< 20), free testosterone 246 pg/mL (<3.0). Ultrasound revealed a hypoechogenic well-circumscribed lesion measuring 2.4 x 1.3 x 2.1 cm within the left testis. The patient underwent a radical left orchiectomy with pathology confirming Leydig cell tumor. Our second case presented at 9 years and 1 month with concern for precocious puberty. On initial exam, right testis long axis diameter measured 2.5 cm (volume of 4 mL) and left measured 2.2 cm, with Tanner 2 pubic hair. Bone age was read as 11 years. Laboratory evaluation showed an LH 0.15 mIU/mL, FSH 1.05 mIU/mL, hCG <5, AFP 2.2 ng/mL (< 9.0), total testosterone 65 ng/dL, free testosterone 3.9 pg/mL. Thyroid and adrenal evaluation were within normal limits. Given the testicular exam and concern for central puberty, he underwent an MRI pituitary which revealed an incidental finding of a sub-centimeter lesion within the mid-to-posterior pituitary gland. A Lupron stimulation test was performed with a non-pubertal peak LH of 4.9 IU/L (< 5 IU/L). Testicular ultrasound revealed a hyperechoic mass with internal vascularity in the right testis. Patient underwent a right testis-sparing enucleation and pathology confirmed a Leydig cell tumor. Discussion: These two cases illustrate the variability in presentation of Leydig cell tumors. The first case demonstrates the classic presentation with peripheral precocious puberty, whereas the second case highlights progression to central precocious puberty, which complicated the diagnostic process. More studies are needed to determine baseline characteristics of Leydig tumors and risk factors for progression to central precocious puberty. Presentation: Sunday, July 13, 2025