12243 The Case of a Metastatic Papillary Thyroid Cancer Presenting as an Unresectable Pelvic Mass

Abstract Disclosure: M. Tucktuck: None. Y. El Soufi: None. O.G. Adeniran: None. A.A. Gliwa: None. Background: Papillary thyroid cancer (PTC) represents around 85% of all thyroid cancers, of which 2-10% of patients will present with metastasis distant to the neck. The frequency of bone metastasis in PTC occurs in only 1-4% of patients. Studies have shown that distant and multi-organ metastasis is associated with higher mortality rates. Clinical case: A 69-year-old woman with diabetes mellitus, cerebrovascular accident, and right lower extremity deep venous thrombosis, presented with right foot and hip pain for 1 week after a mechanical fall. She had a 50 pound weight loss over a year without personal or family history of thyroid cancer or disease or radiation exposure. A soft and nontender mass in the right lower abdomen was noted during a physical exam. Imaging revealed a large heterogeneous lesion (16.3 x 13.3 x 15.5 cm) in the right bony pelvis with internal necrosis, destructing the right iliac bone, and extending into the right sacrum, acetabulum, and musculature, with mass effect on the surrounding vasculature, and enlarged lymph nodes suspicious for metastasis. Thyroid imaging showed a hypervascular hyperechoic 1.3 cm nodule within the right thyroid gland and a large 2 cm left thyroid nodule with scattered microcalcifications. Thyroid function tests were within normal limits. The patient underwent an initial ultrasound guided biopsy of the pelvic mass with indiscriminate results, and later a laparoscopic excisional biopsy of the pelvic mass showed neoplastic papillary proliferation with typical nuclear features, without necrosis or associated ovarian tissue. The immuno-histopathological profile was positive for PAX-8, TTF-1, thyroglobulin, and CK7, and the Ki-67 proliferation index was ∼20-30%. The patient was diagnosed with papillary thyroid cancer with metastasis to the pelvic bone, and was classified as stage IV, cT1bN0M1. As the pelvic mass was inoperable, the patient completed total thyroidectomy and was started on hormone replacement therapy. Subsequent thyroid pathology report was negative for papillary carcinoma. Further review of imaging did not show ectopic thyroid tissue in the neck or an ovarian pathology. Before the patient’s next visit to evaluate for struma ovarii, she passed away. Conclusion: Thyroid cancer is usually treated through thyroidectomy or lobectomy, with radioiodine (RAI) therapy as an effective treatment for differentiated cancers. Our patient, who presented with extremity pain revealing a distant metastasis, completed thyroidectomy with plans to undergo RAI therapy. Our case highlighted the importance of recognizing musculoskeletal presentations as an initial and possibly only finding of a distant metastasis. It also emphasized the utility of multidisciplinary collaboration in detecting and recognizing PTC as a primary thyroid cancer, as early management can reduce mortality and lead to more favorable outcomes. Presentation: 6/2/2024