Chloroquine engages the immune system to eradicate irradiated breast tumors in mice.

Purpose: This study used chloroquine to direct radiation-induced tumor cell death pathways to harness the antitumor activity of the immune system.

Methods And Materials: Chloroquine given immediately after tumor irradiation increased the cure rate of MCaK breast cancer in C3H mice. Chloroquine blocked radiation-induced autophagy and drove MCaK cells into a more rapid apoptotic and more immunogenic form of cell death.