Juvenile Granulosa Cell Tumor as the Presenting Feature of McCune-Albright Syndrome

GNAS mutations have been reported in both McCune-Albright syndrome (MAS) and juvenile granulosa cell tumors (JGCT) but have never been reported simultaneously in the same patient.

A 15-year-old girl developed secondary oligomenorrhea. Laboratory studies revealed suppressed gonadotropin levels with markedly elevated estradiol and inhibin B levels. Pelvic ultrasound showed a 12-cm heterogeneous right adnexal mass; pelvic magnetic resonance imaging to further characterize the mass displayed heterogeneous bilateral femoral bone lesions initially concerning for metastatic disease. Positron emission tomography/computed tomography showed minimal ¹⁸F-fluorodeoxyglucose (FDG) uptake in the pelvic mass but unexpectedly revealed FDG uptake throughout the skeleton, concerning for polyostotic fibrous dysplasia in the context of MAS. The adnexal mass was excised and pathology confirmed a JGCT. The patient's affected bone and JGCT tissue revealed the same pathogenic GNAS p.R201C mutation, while her peripheral blood contained wild-type arginine at codon 201.

This mutation has been previously reported in cases of MAS and JGCT but never simultaneously in the same patient. This demonstration of a GNAS mutation underlying both JGCT and MAS in the same patient raises questions about appropriate surveillance for patients with these conditions.