There was no evidence that associations differed according to MT1R status of the tumor (e.g., <i>P</i><sub>heterogeneity for overall breast cancer</sub> = 0.88).<b>Conclusions:</b> Higher urinary melatonin levels were associated with reduced breast cancer risk in this cohort of postmenopausal women, and the association was not modified by MT1R subtype.<b>Impact:</b> Urinary melatonin levels appear to predict the risk of breast cancer in postmenopausal women.
In the current studies, we have examined the expression of the MT1 receptor in breast cancer cell lines and primary human breast tumors and correlated MT1 receptor expression with the deletion, rearrangement and amplification of the MT1 gene and established markers of breast cancer such as tumor size, stage, estrogen receptor alpha (ERalpha) and progesterone receptor (PR) expression.