title: Medullary thyroid cancer with undetectable serum calcitonin.
abstract: BACKGROUND
  Calcitonin is a sensitive biomarker that is used for diagnosis and follow-up in medullary thyroid cancer (MTC). In patients with tumors > 1 cm, it is uncommon for preoperative serum calcitonin to be in the normal laboratory reference range in patients with MTC, and even more unusual for serum calcitonin to be undetectable.
  
  
  METHODS
  A 39-year-old woman was found to have a left thyroid nodule on magnetic resonance imaging done for neck pain. Ultrasound and fine-needle aspiration biopsy were performed, and cytopathology was positive for malignant cells. The cells also had features suggestive of a neuroendocrine tumor, and the specimen was immune-stained with calcitonin. There was positive immunoreactivity for calcitonin in isolated cells of the cytospin, highly favoring a diagnosis of MTC. Serum calcitonin was < 2 pg/mL (<6 pg/mL), and serum carcinoembryonic antigen was 3.1 ng/mL (<5.2 ng/mL). Given the low calcitonin levels, procalcitonin was also tested and was elevated at 0.21 ng/mL (< 0.1 ng/mL). The patient subsequently underwent a total thyroidectomy and central and ipsilateral lateral lymph node dissection. Histopathology confirmed a 2.6 × 2.0 × 1.2-cm MTC, with strong, diffuse immunostaining for calcitonin. Postoperatively, serum calcitonin has remained undetectable, carcinoembryonic antigen has remained within the reference range, and procalcitonin has become undetectable.
  
  
  CONCLUSIONS
  We present a rare case of a patient with MTC with undetectable preoperative serum calcitonin, whose tumor demonstrated strong, diffuse immunohistochemical staining for calcitonin. We discuss the possible pathogenesis of calcitonin-negative MTC and the challenges in following patients with this condition.
authors.affiliation: Department of Medicine, Division of Endocrinology (E.F.B., M.I.S.), Department of Pathology (A.J.G.), and Department of Otorhinolaryngology (A.B.T.), Montefiore Medical Center, Bronx, New York 10467.
authors.forename: Erika F
authors.initials: EF
authors.lastname: Brutsaert
authors.forename: Adam J
authors.initials: AJ
authors.lastname: Gersten
authors.forename: Andrew B
authors.initials: AB
authors.lastname: Tassler
authors.forename: Martin I
authors.initials: MI
authors.lastname: Surks
mesh_terms: D000328:Adult; D002116:Calcitonin / Q000097:blood*; D018276:Carcinoma, Medullary / Q000097:blood* / Q000473:pathology / Q000601:surgery; D005260:Female; D006801:Humans; D013961:Thyroid Gland / Q000473:pathology / Q000601:surgery; D013964:Thyroid Neoplasms / Q000097:blood* / Q000473:pathology / Q000601:surgery; D013965:Thyroidectomy; D016896:Treatment Outcome
chemical_list: D002116:Calcitonin