Nocturnal urinary 6-sulfatoxymelatonin and mammographic density as a marker of breast cancer risk in postmenopausal women.

B217

Background: Experimental studies have consistently demonstrated anticarcinogenic, antiproliferative, antioxidant, and immunostimulating properties of endogenous melatonin. Epidemiologic studies have investigated the role of melatonin deficiency in the etiology of breast cancer with inconsistent results. Objective: We conducted a cross-sectional study to investigate a potential inverse association between the main urinary metabolite of melatonin, creatinine-adjusted 6-sulfatoxymelatonin (aMT6s) and mammographic breast density (MBD) as a surrogate marker of breast cancer risk. Methods: Women at least one year postmenopausal, not currently on hormone replacement therapy and with no prior diagnosis of cancer, were recruited from a large radiological clinic in Buffalo, New York from March 2005 through August 2005. Breast density and covariate data were collected from current screening mammograms, interviews, questionnaires, anthropometric measures taken during the clinic visit, and overnight urine samples. MBD was measured for 239 women from digitized images utilizing a validated computer-assisted method. Creatinine-adjusted aMT6s was measured by radioimmunoassay. Results : The mean age was 58 (SD 6.0), 30% had BMI (kg/m²) GE 30 and 15% of the women were nulliparous. In a linear model that explained 25.1% of variability in percentage MBD adjusted for age, BMI (kg/m²) and number of full-term pregnancies, we did not observe a significant association between continuous aMT6s and percentage MBD. Using categorical aMT6s in general linear models we observed a marginally significant (p 0.084) association between aMT6s and MBD. Percentage MBD decreased in the top tertile of aMT6s compared to the lowest tertile by 8% in overweight BMI, by 3.6 and 4% in age groups <55 and GE 55 respectively, by 6% in nulliparous women, and by 7.7% in women who used past HRT. Conclusion : The results of this study suggest that melatonin levels influence traditional breast cancer risk factors. More studies are warranted to elucidate associations that may be modified by lifestyle habits to reduce breast cancer risk.