Natural products historically represent a source of clinically approved drugs that have contributed significantly to anticancer drug development. Melaleuca alternifolia Concentration (MAC) is an extract prepared from the native Australian plant M. alternifolia (also a common source of Tea Tree Oil). The anticancer properties of MAC were examined using a spontaneous FVB/N c-neu murine model of breast cancer, with mice receiving intratumoural treatments every 3 days. MAC suppressed tumour growth over a 30 day period and induced cell death through the intrinsic mitochondrial pathway, as determined by the presence of both intramitochondrial superoxide and TUNEL positive regions within MAC treated tumours. Potential immunomodulatory activity of MAC was also examined in the 4T-1 breast cancer model. MAC was associated with an intratumoural increase in the infiltration of CD3+CD4+ and CD3+CD8+ T cell populations as well as a reduction in CD3+CD4+CD25+Foxp3+ regulatory T cells. Furthermore, there was an increase in the presence of Ly6GhiCD11b+ neutrophils in the tumours and bone marrow of MAC treated mice. Intratumourally, MAC was also associated with elevated expression of the co-stimulatory molecule CD80 on Ly6GhiCD11b+MHCII+ cells, indicating the presence of a potential antigen presenting-type neutrophil population. In conclusion, MAC represents a promising anticancer agent through its ability to induce apoptosis via the intrinsic mitochondrial pathway as well as by reducing tumour growth and promoting an anti-tumour immune response in mice.