SAT572 Concomitant Metastatic Hurthle Cell Carcinoma And Rectal Cancer, Challenges In Diagnosis And Management

Disclosure: D. Khurram: None. R. Pansare: None. S.L. Mokshagundam: None. Hurthle cell carcinomas (HCC) are aggressive tumors and account for 5% of follicular cell thyroid malignancies. Tumor size, extra-thyroid extension and distant metastases indicate poor prognosis. 20-30% of HCCs have mets at initial diagnosis, frequent sites being lungs and bones. Metastatic HCCs are exceedingly difficult to manage. Detecting two primary cancers concomitantly is uncommon and poses additional challenges in diagnosis and management. We present an interesting case of HCC with mets to the manubrium, vertebrae, lungs and concomitant rectal adenocarcinoma. A 69-year-old male had MRI spine for back pain which showed multiple lytic osseous lesions within T3 and L1 vertebrae. Further imaging revealed a large lesion in the manubrium. Manubrial mass biopsy was positive for poorly differentiated carcinoma, immunohistochemical staining for CAM5.2, cytokeratin, CD 138, CD56 and TTF-1 (weak). He underwent 6 cycles of palliative chemotherapy with carboplatin and Taxol for carcinoma of unknown origin. PET scan following chemotherapy showed a large heterogenous thyroid mass with intense FDG uptake, along with a suspicious rectal mass. Left thyroid nodule FNA reported Bethesda IV follicular neoplasm, Hurthle cell type. Rectal mass biopsy reported moderately differentiated adenocarcinoma. Histology after total thyroidectomy showed unifocal oncocytic HCC, with lymphovascular invasion but no extrathyroidal extension. Molecular markers showed low TMB, stable microsatellite status, negative PDL-1, negative NTRK fusion and positive ATM E839. He received suppressive dose levothyroxine. Radio-iodine ablation was postponed owing to prioritization of radiation therapy for rectal cancer. Thyroglobulin level increased from 53 ng/ML to 216 ng/ML. He received 149 milli Curies of I131 after Thyrogen stimulation. There was mild radioiodine uptake in the thyroid bed, but the metastatic lesions were not radioiodine avid. Follow-up scans showed multiple bilateral pulmonary nodules with worsening osseous mets. Endoscopic biopsy was consistent with HCC, TTF-1 and PAX8 positive. He was started on Lenvatinib but developed diarrhea, hence switched to Pembrolizumab. Thyroglobulin level improved on Pembrolizumab but was complicated by adrenal insufficiency. For rectal cancer, he received radiation therapy and capecitabine. Our case is interesting for several reasons. Firstly, although bone mets are commonly seen in HCC, manubrial mets, especially as the presenting feature is rare. Secondly, concomitant rectal cancer delayed the treatment of the thyroid cancer. Thirdly, there is no major consensus regarding management of HCC, especially metastatic HCC. HCCs are often not radioactive iodine avid. Combination therapy with Lenvatinib and Pembrolizumab is currently under trial for aggressive thyroid malignancy. It will be interesting to follow the clinical outcomes in this individual. Presentation: Saturday, June 17, 2023