Abstract Disclosure: V. Reddy: None. A. Gowda: None. V. Vattipally: None. D. Kunduru: None. IntroductionSteroid cell tumors(SCT) of the ovary make up less than 0.1% of all ovarian tumors. The three subtypes are stromal luteoma, Leydig cell tumor, and steroid cell tumor-not otherwise specified (NOS) which is the commonest subtype. Androgen excess is seen in 75% tumors and presents with virilization. Tumors are usually benign but maybe malignant in 25-43% cases. Factors predicting malignancy include size >7 cm, mitotic activity, necrosis, hemorrhage, and nuclear atypia. Case ReportA 29 y/o Caucasian female presented with secondary amenorrhea and hirsutism. History includes DM2,hypothyroidism,depression and morbid obesity. She reported early pubarche by age 8,menarche at age 13 and developed hirsutism and irregular menstrual cycles from age 15. No workup due to poor follow up until she saw PCP at age 21.She was diagnosed with PCOS and started on Metformin. Eventually referred to endocrinology at age 27, since amenorrhea and hirsutism persisted. On exam she had significant male pattern hair loss and hirsutism over face and body.She reported three first trimester miscarriages.Labs showed testosterone 370 ng/dl, 17 OHP 808 ng/dl, DHEAS 47 ng/dl, Estradiol 117 pg/ml, FSH 2.2 mIU/ml, LH 2.5 mIU/ml, androstenedione 319 ng/dl.Transvaginal US was unremarkable. She was diagnosed with non classical adrenal hyperplasia (NCAH) and started on treatment with prednisone 5 mg daily, drospirenone and spironolactone 100 mg daily.3 months later, labs showed 50% lowering of testosterone to 199 ng/dl and 17 OHP to 407 ng/dl.There was continued biochemical and clinical improvement at the next visit with 17 OHP 73 ng/dl and testosterone 55 ng/dl. Labs done 21 months after initial presentation, showed sudden dramatic rise in 17 OHP to 1148 ng/dl and testosterone to 639 ng/dl. Normal AFP, HCG, CEA, CA125, CA19-9, Inhibin A. CT showed 10.4 cm solid right ovarian mass and underwent right salpingo-oophorectomy. Pathology showed steroid cell tumor, NOS. Labs 1 month postoperatively showed complete normalization of testosterone to <3 ng/dl, 17 OHP to 11 ng/dl and DHEAS 0.66 ng/dl. Steroid therapy was tapered and discontinued. DiscussionWe present the case of a patient with ovarian SCT presenting as NCAH.SCTs are very rare accounting for only 0.1% of all ovarian tumors. Since they commonly secrete androgens, they present similarly to CAH or PCOS and may rarely even co-exist with CAH. Differentiating between NCAH and SCT is difficult especially when there is initial response to steroid therapy and imaging is unremarkable as with our patient. It is important to consider SCT in patients with hyperandrogenism even in the setting of elevated 17 OHP levels. Care should be taken to follow up both clinical and metabolic metrics closely and investigate if any change is noticed. Early diagnosis can prevent irreversible symptoms of hyperandrogenism. Presentation: 6/1/2024