Melatonin counteracts tumor occurrence and tumor cell progression in vivo and in vitro in animal and human breast cancer cell cultures. The action occurs predominantly through its Melatonin MT1 Receptor. This study examined the presence or absence of the MT1 Melatonin Receptors in 167 Triple Negative [TNBC (ER, PR, and Her-2/neu phenotype negative)] Human Breast Carcinomas. The MT1 receptor immunostain was evaluated semiquantitatively as staining intensity (0, 1, 2, 3), percentage of stained cells and the weighted index (WI - staining intensity times percentage of stained cells). A score of WI < 60 was regarded as “negative”. There was a statistically significant difference in incidence of MT1 postivity and staining intensity between carcinomas in African American (AA) and Caucasian (C) women. The AA showed a higher incidence of MT1 negative tumors (48.8% in AA compared to 11.8% in C) and a lower average WI. In both groups of women the younger age group (<50 yrs of age at diagnosis) had a lower average WI (in <50 yr olds 69.1 in AA, 138.5 in C; in >50 yr olds of 75.3 in AA, 170.6 in C). In multivariate survival analysis, MT1 negative TNBC in all cases regardless of race showed a significantly higher hazard ratio for disease progression, shorter progression free survival, disease related death, and overall survival. These results suggest that melatonin or a melatonin receptor agonist may be useful biologic additions in the treatment of some forms of TNBC, especially in AA women who show a more aggressive disease course.