EP40 – Colorectal Adenocarcinoma Masquerading as Thyroid Cancer

      Simon, Rebecca1; Sulanc, Ebru1; Bhan, Arti1 1 Division of Endocrinology, Diabetes, Bone and Mineral Disorders, Henry Ford Hospital, Detroit, MI, USA   Background: Metastasis to the thyroid gland is unusual, due to an unfavorable local micro-environment that limits cancer cell survival1. Microscopic metastases to the thyroid gland have been reported in 4-9% of autopsies. The most common primary malignancies were lung, breast, melanoma, and kidney2.  Colon adenocarcinoma metastasis to the thyroid, in particular, is rarely described. Case Report: A 55 year-old woman was found to have a mass on screening colonoscopy in 2012. Resection revealed a 2.8 cm moderately differentiated adenocarcinoma without lymph node involvement. Imaging revealed no evidence of metastases so she was monitored yearly. In 2013, she was diagnosed with Graves’ disease, treated with radioactive iodine. In 2015, a rising CEA level prompted a PET-CT, revealing a hypermetabolic left thyroid nodule. Fine needle aspiration (FNA) was read as papillary thyroid carcinoma (PTC) based on morphologic features. She underwent thyroidectomy and on immunophenotyping, the tumor cells stained positive for CK20 and CDX2, consistent with metastatic colorectal adenocarcinoma. A secondary review of her FNA was done and Pathology agreed it was consistent with adenocarcinoma. Radioactive iodine treatment caused cell shrinkage and resultant nuclear enlargement that gave a morphologic appearance of PTC. This was felt have contributed to the initial false pathology report. The development of a thyroid nodule in patients with prior malignancy poses a diagnostic challenge, especially since we do not routinely perform special stains to delineate other cancers. This case demonstrates that a high index of suspicion is needed when patients present with a thyroid nodule in the setting of other known malignancy.   References:
    1. Cherk MH, Moore M, Serpell J, Swain S, Topliss DJ. Metastatic colorectal cancer to a primary thyroid cancer. World Journal of Surgical Oncology. 2008;6:122. doi:10.1186/1477-7819-6-122.
    2. Shimaoka K, Sokal JE, Pickren JW: Metastatic neoplasms in the thyroid gland. Pathological and clinical findings. Cancer 1962, 15:557-565.


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