The disclosure concerns a method for cancer treatment by in vivo priming and activation of natural killer cells for achieving tumor cell lysis. The method includes introducing into a patient a priming tumor cell preparation (PTCP) derived from a first tumor cell line, which is irradiated to inactivate the first tumor cells or a membrane preparation thereof, the first tumor cells having known priming ligands on the membrane surface thereof. The patient's rest NK cells are contacted by the PTCP in vivo, resulting in primed NK cells, which are characterized by upregulation of CD69, shedding of CD16, or a combination of CD69+ and CD16−. These primed NK cells then contact second tumor cells, the cancer, and are configured to lyse and kill the second tumor cells.