title: Metastatic colorectal cancer to a primary thyroid cancer.
abstract: BACKGROUND
  Metastatic malignancy to the thyroid gland is generally uncommon due to an unfavourable local thyroid micro-environment which impairs the ability of metastatic cells to settle and thrive. Metastases to the thyroid gland have however been reported to occur occasionally particularly if there has been disruption to normal thyroid tissue architecture.
  
  
  METHODS
  We report a patient with a history of surgically resected rectal adenocarcinoma who presents with a rising serum CEA level and an 18F-FDG PET scan positive thyroid nodule which was subsequently confirmed at surgery to be a focus of metastatic rectal adenocarcinoma within a primary poorly differentiated papillary thyroid carcinoma.Subsequent treatment involved right hemi-thyroidectomy, pulmonary wedge resection of oligometastatic metastatic colorectal cancer and chemotherapy.
  
  
  CONCLUSIONS
  Metastatic rectal carcinoma to the thyroid gland and in particular to a primary thyroid malignancy is rare and unusual. Prognosis is likely to be more dependent on underlying metastatic disease rather than the primary thyroid malignancy hence primary treatments should be tailored towards treating and controlling metastatic disease and less emphasis placed on the primary thyroid malignancy.
authors.affiliation: Department of Nuclear Medicine, the Alfred Hospital, Commercial Road, Melbourne Victoria 3004, Australia. m_cherk@yahoo.com.au
authors.forename: Martin H
authors.initials: MH
authors.lastname: Cherk
authors.forename: Maggie
authors.initials: M
authors.lastname: Moore
authors.forename: Jonathan
authors.initials: J
authors.lastname: Serpell
authors.forename: Sarah
authors.initials: S
authors.lastname: Swain
authors.forename: Duncan J
authors.initials: DJ
authors.lastname: Topliss
mesh_terms: D015179:Colorectal Neoplasms / Q000473:pathology*; D019788:Fluorodeoxyglucose F18; D006801:Humans; D008297:Male; D008875:Middle Aged; D049268:Positron-Emission Tomography; D013964:Thyroid Neoplasms / Q000556:secondary*
chemical_list: D019788:Fluorodeoxyglucose F18