title: Reliability of urinary 6-sulfatoxymelatonin as a biomarker in breast cancer.
abstract: The objective of this study is to evaluate the effect of cryopreservation at different storage temperatures on urinary 6-sulfatoxymelatonin (aMT6s) concentration. Overnight urine from 28 postmenopausal women participating in the ORDET cohort study was filtered and separated into 6 mL aliquots. Urine samples were stored at -80 degrees C and at -30 degrees C for an average of 14 years. Urinary aMT6s concentration was assessed using a competitive immunoassay. Mean aMT6s values of samples stored at -30 degrees C were systematically lower than those of samples stored at -80 degrees C (10.7 ng/mL versus 15.8 ng/mL, p<0.001). Bland Altman plots showed disagreement between determinations at different storage temperatures at the highest levels of the metabolite concentration. The degree of agreement evaluated in terms of intraclass correlation coefficient was 0.68 (95% CI 0.41-0.84, p<0.0001). Pearson's correlation coefficient between aMT6s values of the two differently stored samples was 0.93 (p<0.001), while the Kendal tau coefficient for rank distribution was 0.73 (p<0.001). Our data suggest that storage temperatures might affect degradation of aMT6s during storage. However, individual characterization by melatonin levels does not seem to be affected by cryopreservation conditions.
authors.affiliation: Department of Epidemiology, Regina Elena Cancer Institute, Rome, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Barba
authors.forename: A
authors.initials: A
authors.lastname: Cavalleri
authors.forename: H J
authors.initials: HJ
authors.lastname: Schünemann
authors.forename: V
authors.initials: V
authors.lastname: Krogh
authors.forename: A
authors.initials: A
authors.lastname: Evangelista
authors.forename: G
authors.initials: G
authors.lastname: Secreto
authors.forename: A
authors.initials: A
authors.lastname: Micheli
authors.forename: Q
authors.initials: Q
authors.lastname: Zhou
authors.forename: B
authors.initials: B
authors.lastname: Fuhrman
authors.forename: B
authors.initials: B
authors.lastname: Teter
authors.forename: F
authors.initials: F
authors.lastname: Berrino
authors.forename: P
authors.initials: P
authors.lastname: Muti
mesh_terms: D000328:Adult; D000368:Aged; D014408:Biomarkers, Tumor / Q000652:urine*; D001943:Breast Neoplasms / Q000652:urine*; D015925:Cryopreservation; D005260:Female; D006801:Humans; D008550:Melatonin / Q000031:analogs & derivatives* / Q000737:chemistry / Q000652:urine; D008875:Middle Aged; D013048:Specimen Handling; D013696:Temperature
chemical_list: D014408:Biomarkers, Tumor; C054513:6-sulfatoxymelatonin; D008550:Melatonin