Malignant transformation of the cells in cancer is caused by excessive proliferation accompanied by diminished ability for apoptosis due to the loss of normal control on these processes. Despite their ubiquity calcium ions are central to both processes, serving as major signalling agents. The present review examines what changes in calcium distribution among various compartments: extracellular space, cytoplasm, endoplasmic reticulum and mitochondria take place during transition from normal to pathological cell growth and death, what Ca2+-handling proteins are involved, and how this affects spatial and temporal characteristics of Ca2+ signals aimed at regulating specific cellular responses. Uncovering the underlying molecular events may help elaborating new strategies for cancers treatment.