•Sigma 1 Receptor mediates cancer-specific apoptosis induced by combination treatment with p53 plus Rimcazole.•ROS production and ER stress are induced by combination treatment with p53 plus Rimcazole.•Calcium mobilization is induced by combination treatment with p53 plus Rimcazole.•p38 MAPK is activated by combination treatment with p53 plus Rimcazole.•p53 plus Rimcazole induces activation of caspase-3 and the upregulation of Bax. Over the last years, many improvements have been made in the treatment of breast cancer; however, novel and less toxic therapies are still needed, especially for relapsing and chemo-resistant patients. Here, we analyzed the therapeutic potential of p53 and Rimcazole, a Sigma 1 Receptor antagonist. Rimcazole and p53 are being evaluated in preclinical and clinical trials, respectively. While p53 is a promising antitumor therapeutic agent, antagonists of Sigma 1 Receptor also inhibit tumor cell survival and induce apoptosis. Our current study demonstrates for the first time the synergistic effect of p53 in combination with the Sigma 1 Receptor antagonist Rimcazole. Furthermore, we show that shRNA knockdown of Sigma 1 Receptor in combination with p53, lead to a similar synergistic effect, and that this synergistic effect, in breast cancer growth suppression occurs independent of p53 status. Furthermore, this combination treatment induced ER stress, p38 MAPK activation, ROS production, and proteins involved in apoptosis (caspases-3, Bax) in breast cancer cells. Combining these therapeutic anti-cancer molecules provides an innovative approach for potentially treating human breast cancer.