PRKAA1 and neoplasm: In the present study, we investigated the efficacy of phenformin in preventing or repressing the growth of tumour xenografts derived from oestrogen receptor (ER)-positive luminal-type MCF7 and receptor triple-negative MDAMB231 breast cancer cell lines and examined the tumour-specific and systemic effects of phenformin on cell proliferation and components of the AMPK and the cell-cycle pathways.