For example, a cell line which is believed to be of human breast cancer may actually be the cell line of a human prostate cancer, mouse or Syrian hamster.

Cell line contamination is not uncommon incident in a laboratory handling more than one cell line. Cell line contamination may also be caused by the transformation of host cells by the injected human tumor cells. Human tumors injected into nude murine animals may transform host cells and the tumor growing in the host animal may be a mixture of human and murine cells or purely of murine origin (Oncol Res 9:433-438, 1997; Br J Cancer 76:1134-1138, 1997). Inter- or intraspecies cell line contamination can easily be identified by conventional and molecular cytogenetics. It can save valuable time, effort, and precious research funds and prevent investigators from innocently publishing erroneous molecular data and misleading conclusions.