Presentation of comet assay data by using a five-grade scale. The comets are classified according to extent of DNA in tail and a value 0-4 is given (0: almost no DNA in tail, 4: almost the entire DNA in tail). By measuring 100 comets, an overall score between 0 and 400 arbitrary units is calculated. A: Treatment with cisplatin in colorectal cancer cell lines. B: Treatment with melphalan in breast cancer cell lines C: Treatment with mechlorethamine in breast cancer cell lines D: Treatment with doxorubicin in breast cancer cell lines.