Chromosomal instability (CIN) refers to an increased rate of changes in the number or structure of chromosomes within a cell. This condition can lead to an abnormal distribution of chromosomes during cell division, resulting in cells with missing, extra, or rearranged chromosomes. CIN is often associated with various types of cancer, as it can contribute to tumor progression and resistance to treatment. CIN can arise from several factors, including defects in the mechanisms that ensure accurate chromosome segregation, such as the spindle assembly checkpoint. Cells exhibiting CIN may show a higher mutation rate, which can further drive the development of malignancies. Understanding CIN is crucial for developing targeted therapies in cancer treatment.