MTNR1A and breast carcinoma: A negative correlation between melatonin receptor expression and cancer has also been observed in Oral Squamous Cell Carcinoma (OSCC), where a reduced expression of MT1 is also related to the T stage of tumor [186], and in breast cancer, where a lower MT1 expression is associated with a poorer prognosis [156], together with a higher tumor grade and TNM staging [187].