6802 NRAS-Mutated Malignant Struma Ovarii with Papillary and Solid Histologic Variants

Abstract Disclosure: S. Wagle: None. L. Lomo: None. R.L. Dood: None. B. Chadwick: None. D. Abraham: None. Introduction: Struma ovarii is a mono-dermal teratoma of the ovary that is composed of more than >50% of mature thyroid tissue. It accounts for 5% of ovarian teratomas and 1% of ovarian tumors. Although rare, it is seen in women between 40-60 years of age. Most of these tumors are found incidentally. Malignant struma ovarii is even rarer and the mutational profile of these tumors is neither well studied nor understood. We present an uncommon case of malignant struma with NRAS p.Q61R mutation yet with papillary and solid histologic patterns. Case Description: A 53-year-old female with no significant medical or family history presented with acute worsening of chronic lower abdominal pain and irregular menstruation. Her symptoms developed gradually over 6 months. A pelvic and abdominal CT identified a 9.7 cm cystic left ovarian mass without evidence of ascites or peritoneal masses. She underwent laparoscopic left salpingo-oophorectomy. Histopathology examination of the ovarian tumor revealed classical type, well-differentiated papillary, and solid patterns of thyroid carcinoma. The cells revealed nuclear enlargement, irregular nuclei, finely dispersed chromatin, distinct nucleoli, and nuclear grooves. Due to the histologic pattern of classical papillary thyroid cancer, BRAF V600E pyrosequencing was conducted, which revealed wild-type BRAF. This was followed by NGS when NRAS p.Q61R pathogenic variant was identified. Her thyroid ultrasound did not reveal actionable nodules. A TSH (2.17mU/ml) and thyroglobulin (7.6 ng/ml, TG ab neg) levels are consistent with a normal functioning thyroid gland. This patient's tumor findings are unique in that papillary thyroid carcinoma (PTC) and solid growth patterns are typically associated with the BRAF V600E mutation but rarely seen in the context of an RAS mutation. Discussion: Typically, thyroid cancers with papillary and solid variant features are associated with the BRAF V600E mutation. RAS-type tumors have follicular histologic architecture. BRAF and RAS mutations are mutually exclusive in tumors. Our patient’s malignant struma is unique in that it contained a wild-type BRAF and was positive for NRAS p.Q61R mutation. However, the histology was that of papillary and solid patterns. NRAS mutation with papillary histology combination is rare and is seen in 12% of thyroid cancers. The mutational profile of malignant struma ovarii has not been fully understood or studied due to their rarity. Presentation: 6/3/2024