A novel family of human mitochondrial RNAs, referred to as chimeric RNAs, which are differentially expressed in normal, pre-cancer and cancer cells, are described. Oligonucleotides targeted to the chimeric RNAs are provided. The described oligonucleotides or their analogs can be used for cancer diagnostics and cancer therapy as well as for research. In one embodiment of this invention, these oligonucleotides hybridize with the sense or with the antisense mitochondrial chimeric RNAs, and the result of the hybridization is useful to differentiate between normal proliferating cells, pre-cancer cells and cancer cells. In another embodiment of the invention, the compositions comprise oligonucleotides that hybridize with the human chimeric RNAs resulting in cancer cell and pre-cancer cell death, while there is no effect in normal cells, constituting therefore, a novel approach for cancer therapy.