Abstract #1405977: Follicular Thyroid Cancer Presenting as Atypical Femur Fracture

Follicular thyroid cancer (FTC) is the second most common thyroid cancer and is known to metastasize hematogenously. The incidence of distance metastasis in FTC is approximately 6%-20% with bones and the lungs being the most common sites. Outcomes for patients with metastatic follicular thyroid cancer are poor, with a 10-year survival of 41%. 54-year-old female presented to endocrine clinic following an atypical fracture to her lesser trochanter. This occurred while applying minor force to the brake pedal in her car. Further evaluation with imaging revealed a 3.5cm boney lesion and a bone biopsy was consistent with metastatic follicular thyroid cancer. Her history included a left hemithyroidectomy in 2014 for a 5.2cm nodule that pathology initially reported as follicular adenoma. She was not followed by endocrinology after surgery. Ultrasound in 2013 showed two subcm right thyroid nodules. In 2022, she underwent FNA of two thyroid nodules and lymph nodes. She had a 0.9cm isthmus nodule that was suspicious for malignancy, 0.7cm right lower pole thyroid nodule that was benign. Two lymph nodes were also benign, but had Tg levels of 8 and 2ng/mL. Her imaging also showed pulmonary nodules and a right parietal bone lesion. She underwent completion thyroidectomy with bilateral central neck dissection and right lateral neck dissection. Pathology confirmed PTC follicular variant 0.6cm unifocal lesion in the right lobe with no angioinvasion, lymphatic invasion and no ETE. 53 lymph nodes were all negative. Due to her known distant disease, she is stage IVc. Pathology believes her bone lesion is consistent with the 0.6cm lesion and not the prior 5.2cm left nodule. She underwent treatment with I-131 with 198mCi. Post scan showed uptake in the left thyroid bed, right parietal bone and left lesser trochanter. Lung nodules did not demonstrate iodine avidity. Tg Levels prior to surgery was 2421. At time of RAI Tg was 2927 and was down to 234.6 three months after RAI. This patient was found to have boney metastasis of follicular thyroid cancer after presenting with an atypical femur fracture. This diagnosis was confirmed with her bone biopsy followed by pathology of the thyroid. RAI therapy is the most effective treatment for metastatic disease but its effect depends on the extent of uptake. Other treatments include surgery pending the location, or external beam radiation. This case highlights how a small follicular cancer can present with metastatic disease, causing morbidity for patients such as atypical fractures and pain.