title: Measurement of calcitonin and calcitonin gene-related peptide mRNA refines the management of patients with medullary thyroid cancer and may replace calcitonin-stimulation tests.
abstract: BACKGROUND
  Serum calcitonin (sCT) is the main tumor marker for medullary thyroid cancer (MTC), but it has certain limitations. Various sCT assays may have important intra-assay or interassay variation and may yield different and sometimes conflicting results. A pentagastrin- or calcium-stimulation calcitonin (CT) test may be desirable in some situations. Alternatively, or in the absence of the stimulation test, mRNA detection offers the advantages of being more comfortable and less invasive; it only requires blood collection and has no side effects. The objective of this study was to investigate the applicability of measuring calcitonin-related polypeptide alpha (CALCA) gene transcripts (CT-CALCA and calcitonin gene-related peptide [CGRP]-CALCA) in patients with MTC and in relatives diagnosed with a RET mutation and to test mRNA as an alternative diagnostic tool for the calcitonin-stimulation test.
  
  
  METHODS
  Twenty-three healthy controls and 26 individuals evaluated for MTC were selected, including patients with sporadic or hereditary MTC and RET mutation-carrying relatives. For molecular analysis, RNA was extracted from peripheral blood, followed by cDNA synthesis using 3.5 μg of total RNA. Quantitative real-time polymerase chain reaction (RT-qPCR) was performed with SYBR Green and 200 nM of each primer for the two specific mRNA targets (CT-CALCA or CGRP-CALCA) and normalized with the ribosomal protein S8 as the reference gene.
  
  
  RESULTS
  We detected CALCA transcripts in the blood samples and observed a positive correlation between them (r=0.946, p<0.0001). Both mRNAs also correlated with sCT (CT-CALCA, r=0.713, p<0.0001; CGRP-CALCA, r=0.714, p<0.0001). The relative expression of CT-CALCA and CGRP-CALCA presented higher clinical sensitivity (86.67 and 100, respectively), specificity (97.06 and 97.06), positive predictive value (92.86 and 93.75), and negative predictive value (94.29 and 100), than did sCT (73.33, 82.35, 64.71, and 87.50, respectively). In addition, the CALCA transcript measurement mirrored the response to the pentagastrin test.
  
  
  CONCLUSIONS
  We demonstrate that the measurement of CALCA gene transcripts in the bloodstream is feasible and may refine the management of patients with MTC and RET mutation-carrying relatives. We propose considering the application of this diagnostic tool as an alternative to the calcitonin-stimulation test.
authors.affiliation: Laboratory of Molecular and Translational Endocrinology, Department of Medicine, Escola Paulista de Medicina, Federal University of São Paulo, São Paulo, Brazil.
authors.forename: Cléber P
authors.initials: CP
authors.lastname: Camacho
authors.forename: Susan C
authors.initials: SC
authors.lastname: Lindsey
authors.forename: Maria Clara C
authors.initials: MC
authors.lastname: Melo
authors.forename: Ji H
authors.initials: JH
authors.lastname: Yang
authors.forename: Fausto
authors.initials: F
authors.lastname: Germano-Neto
authors.forename: Flávia de O F
authors.initials: Fde O
authors.lastname: Valente
authors.forename: Thiago R N
authors.initials: TR
authors.lastname: Lima
authors.forename: Rosa Paula M
authors.initials: RP
authors.lastname: Biscolla
authors.forename: José G H
authors.initials: JG
authors.lastname: Vieira
authors.forename: Janete M
authors.initials: JM
authors.lastname: Cerutti
authors.forename: Magnus R
authors.initials: MR
authors.lastname: Dias-da-Silva
authors.forename: Rui M B
authors.initials: RM
authors.lastname: Maciel
mesh_terms: D014408:Biomarkers, Tumor / Q000378:metabolism; D002116:Calcitonin / Q000097:blood* / Q000235:genetics; D015740:Calcitonin Gene-Related Peptide / Q000097:blood* / Q000235:genetics; D018278:Carcinoma, Neuroendocrine; D016022:Case-Control Studies; D018076:DNA, Complementary / Q000378:metabolism; D005260:Female; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008297:Male; D009154:Mutation; D010418:Pentagastrin / Q000378:metabolism; D011237:Predictive Value of Tests; D011498:Protein Precursors / Q000235:genetics; D051096:Proto-Oncogene Proteins c-ret / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism; D012680:Sensitivity and Specificity; D013964:Thyroid Neoplasms / Q000235:genetics* / Q000378:metabolism*
chemical_list: D014408:Biomarkers, Tumor; C000606589:CALCA protein, human; D018076:DNA, Complementary; D011498:Protein Precursors; D012333:RNA, Messenger; D002116:Calcitonin; D051096:Proto-Oncogene Proteins c-ret; C099282:RET protein, human; D010418:Pentagastrin; D015740:Calcitonin Gene-Related Peptide