RB1 and cancer: Likewise, chromosome content in cancer lines is aneuploid (abnormal chromosome content) and heteroploid (variability in chromosome number in the same cell population) as a result of alteration of tumor suppressor proteins, i.e., p53 and Rb, leading to genetic instability throughout the subcultures.76 Viability and karyotype have also been used to check the genetic stability of cell cultures and to see if cells have changed.77