Metastatic Medullary Thyroid Carcinoma Without Identifiable Primary Tumor Within the Thyroid Gland, Presenting with Initial Lymph Node Metastasis Followed by Distant Peritoneal Metastasis: A Case Report of a Rare Phenomenon. - Lee, Eunyeong; Byun, Jungsup; Kim, Moonsik; Kim, Jae-Hui; Park, Ji-Young; Park, Jongmin; Seo, An Na (Journal of Clinical Medicine, 2026)