MTNR1B and breast carcinoma: Another study evaluated the association between breast cancer risk and common single nucleotide polymorphismsin the MTNR1a, MTNR1b, and AANAT (encoding arylalkylamine N-acetyltransferase) genes among 2,073 cases and 2,083 controls, and reported that common genetic variation in the MTNR1a and MTNR1b genes might contribute to breast cancer susceptibility, and the associations might vary with menopausal status [27].